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MERRILL-PALMER QUARTERLY, VOL. 50, NO. 3
387
Deborah Lowe Vandell, Department of Educational Psychology
The support (U10-HD027040) from the National Institute of Child Health and Human
Development is much appreciated. I also am grateful to my collaborators on the NICHD
Study of Early Child Care who have challenged and shaped my thinking about child care and
developmental processes. It has been a privilege to be a part of that group. Finally, I thank
Kim Pierce for her comments and feedback about earlier drafts of this paper.
Correspondence concerning this article should be addressed to Deborah Lowe Van-
dell, Department of Educational Psychology, 1025 West Johnson Street, Madison, WI
53706. E-mail: dvandell@wisc.edu.
Merrill-Palmer Quarterly, July 2004, Vol. 50, No. 3, pp. 387–414. Copyright © 2004 by
Wayne State University Press, Detroit, MI 48201.
Early Child Care: The Known
and the Unknown
Deborah Lowe Vandell, University of Wisconsin–Madison
Child care research during the last 20 years has made considerable progress in
addressing questions about (a) the effects of child care quality, (b) the effects of
amount and timing of early child care, and (c) the effects of different types of
care such as centers, child care homes, and relative care. This commentary
summarizes the converging research evidence with respect to each of these
questions and then outlines some future directions for child care research.
The second half of the 20th century witnessed substantial changes
in the lives of young children as maternal employment increased and
more children participated in nonparental care arrangements. The
available evidence indicates that these care arrangements vary widely in
quality, amount, and type (National Institute of Child Health and
Human Development Early Child Care Research Network [NICHD
ECCRN], 1996; 2000a; U.S. Census Bureau, 2003). These variations
and the large number of children in care (over 10 million children in
the United States in 1999) have raised several questions: (a) Does qual-
ity of early child care matter? (b) Does amount and timing of early
child care matter? and (c) Does type of early child care matter?
Answers to these questions are important for parents and policymak-
ers who are interested in the individual and collective well-being of
children. They also are important for developmental theory because of
their relevance to fundamental issues in the discipline such as the role
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388 Merrill-Palmer Quarterly
of early versus later experience and the efficacy of enrichment and
intervention efforts.
In this commentary, I have two goals. My first goal is to summa-
rize the converging research evidence with respect to the three ques-
tions about child care. The evidence from scores of studies represents
what we currently know about the effects of child care on child devel-
opmental outcomes. The evidence presented is not exhaustive, but
illustrative. My second goal is to consider areas that are unresolved or
have not yet been examined. These unknowns, I believe, represent next
steps for child care research.
The need for data to address the questions about early child care
was one reason that the NICHD Study of Early Child Care (SECC)
was created (NICHD ECCRN, 2001c). Key elements in the design of
the SECC included (a) a sufficiently large sample (n= 1,364) to detect
effects; (b) a diverse sample that included children of color (24%),
mothers with less than a high school education (11%), and single-
parent households (14%); (c) robust longitudinal measures of child
care quality, amount, timing, and type (e.g., center, family day care
home, nanny); (d) measures of children’s social, cognitive, and lan-
guage development, obtained during infancy, early childhood, and
middle childhood by multiple methods; (e) extensive family measures
collected shortly after the child’s birth to use as controls for selection
bias; and (f) longitudinal family assessments to evaluate changes in
family functioning in response to child care.
The NICHD Early Child Care Research Network (ECCRN), the
name adopted by the investigators who work collectively on papers
from the SECC, has now considered the effects of quality, amount and
timing, and types of care in a series of papers that examined children’s
attachment to mother (1997b, 2001b), mother-child interactions
(1999a, 2003c), peer interactions (2001a), behavior problems (1998,
2002b, 2003a), social competence (1998, 2002b, 2003c), and cognitive,
language, and preacademic performance (2000b, 2002b). Other investi-
gators (Brooks-Gunn, Han, & Waldfogel, 2002; Sagi, Koren-Karie,
Gini, Ziv, & Joels, 2002) have used the SECC data set to address related
questions. Instructions for obtaining copies of the public use data set
can be found at http://secc.rti.org/.
In addition to the SECC, other large, multisite studies include the
Cost, Quality, and Outcomes Study (Peisner-Feinberg et al., 2001), the
Family and Relative Care Study (Kontos, Howes, Shinn, & Galinsky,
1995), the National Day Care Study (Ruopp, Travers, Glantz, & Coelen,
1979), and the Child-Care Staffing Study (Howes, Phillips, & White-
book, 1992). These studies have focused on particular types of care.
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Early Child Care 389
Challenges and Cautions
Before examining the progress in answering the child care ques-
tions, several overarching challenges and accompanying cautions
should be noted. The first challenge is that most child care research is
correlational. As is the case with any correlational evidence, there are
concerns that sample selection and omitted variables may explain
obtained relations. For example, if educationally minded parents place
their children in more cognitively stimulating child care settings, then
an apparent relation between cognitively stimulating child care and
children’s academic skills may be explained by these preexisting family
differences. Or, if parents place children who are challenging or diffi-
cult in child care for more hours than less difficult children, then a rela-
tion between child care hours and problem behaviors may be explained
by this preexisting child difference. The challenge, then, is to reduce the
likelihood that child care effects are explained by these other factors.
One way of addressing this problem has been to adopt experimental
designs in which children are randomly assigned to child care of varying
types and quality. In several studies that are discussed later in this paper
(e.g., Campbell & Ramey, 1994; Schweinhart, Weikart, & Larner, 1986),
experimental designs were used to examine the effects of high-quality
center-based programs for children who were at risk for school failure.
In other research also to be reviewed (Ruopp et al., 1979), two aspects of
child care quality—child-adult ratio and caregiver education and train-
ing—were experimentally manipulated to determine their effects on
children’s cognitive and social functioning. To my knowledge, no one
has studied the effects of amount/timing in an experimental study.
In the absence of random assignment experiments, researchers
have adopted other strategies to minimize selection bias and omitted
variables. One strategy, which was first used in the 1980s and has since
become standard practice, is to include family and child measures as
covariates. The early studies typically controlled for a limited number
of demographic factors such as maternal education and child gender.
Recent research, however, has incorporated extensive covariates.
In the SECC (NICHD ECCRN & Duncan, 2003), the sizes of
child care coefficients were compared in statistical analyses that
included no covariates, a limited number of family and child covari-
ates, and extensive covariates. The size of the child care coefficients was
substantially reduced when the demographic covariates were added to
the base model, indicating that the base model containing no covari-
ates was biased. The inclusion of more extensive measures of family
functioning to the demographic variables, in contrast, resulted in little
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390 Merrill-Palmer Quarterly
or no change in the size of the child care coefficients, suggesting that it
was unlikely that unobserved family characteristics could account for
the obtained child care effects.
Although the use of multiple covariates reduces the likelihood that
obtained relations can be explained by omitted variables, it has its own
limitations. Because only the unique variance is attributed to child care
and all shared variance is attributed to other factors, the strategy yields a
conservative estimate of effects. Thus, investigators may be controlling
for and thereby removing the very effects of interest (Newcomb, 2003).
Another strategy to minimize the likelihood that omitted or
unmeasured factors account for obtained child care effects has been to
use children’s prior performance as a control. Analyses of this sort used
in the SECC (NICHD ECCRN & Duncan, 2003) and the Cost, Qual-
ity, and Outcomes Study (Peisner-Feinberg et al., 2001) have asked if a
particular child developmental outcome is predicted by quality,
amount/timing, or type of care when the child’s prior performance is
included as a covariate. These residual change analyses are better able
to adjust for observed and unobserved factors, but have less power,
than simply controlling for family and child demographic factors.
A second challenge is that child care is a complex phenomenon that
varies along multiple dimensions. Because research initially focused on
quality or type or amount, it was not possible to ascertain if ostensible
effects of quality were actually effects of quantity or type; or, if ostensi-
ble effects of quantity could be explained by the type or quality of the
care. Consequently, recent research such as the SECC has sought to
examine effects of one aspect of care while controlling for other aspects.
A third challenge and caution is the (obvious) caveat that our
research evidence is based on the particular samples of children who
have been studied in child care of particular quality, amount, and type.
If families with impoverished circumstances (or more affluent circum-
stances) are not included in research studies, then our ability to
understand child care effects in those circumstances is reduced. Under-
standing the effects of child care also requires sampling across the full
array of child care variations. We are likely to underestimate child care
effects if analyses are based on a restricted range of quality, hours, or
types of care. One reason that research studies conducted in Sweden
generally failed to find quality effects may be that the quality was uni-
formly high. Consistent with this point, Sagi et al. (2002) noted that
child-adult ratio in centers was not related to attachment security in
separate analyses involving the NICHD SECC and the Haifa Study of
Early Child Care. However, when the two samples were combined and
a broader range of child-adult ratios was tested, relations between
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Early Child Care 391
ratios and attachment were detected. In the SECC, it is likely that the
effects associated with quality were underestimated because refusal
rates were higher for informal care settings and settings that were car-
ing for children of low-income families. Consistent with this point,
child outcomes in the SECC were significantly lower for children who
attended child care settings that were not observed (NICHD ECCRN
& Duncan, 2003).
With these challenges, limitations, and caveats in mind, let us now
consider the first of our three questions.
Does Quality of Child Care Matter?
An indication of our progress in addressing the quality question is
clear when we recall Belsky and Steinberg’s classic review published in
1978. In that review of the extant literature of the time, some 40 stud-
ies, Belsky and Steinberg observed, “Our actual knowledge of its [day
care] effects is exceedingly limited. Generally investigations have been
conducted within high-quality centers which are not representative of
most substitute-care environments” (p. 929). This dearth of research
led them to conclude, “The findings from existing research on day care
may not be generalizable to the kind and quality of care available to
most of the nation’s families” (p. 930).
The need to understand the effects of child care quality motivated
much of the research during the next 25 years. Early studies by Howes
(1983), Clarke-Stewart (1987), Phillips, McCartney, and Scarr (1987),
and Vandell and Powers (1983) observed children in child care and
recorded their experiences. High-quality child care was conceptualized
as involving supportive interactions with caregivers, positive interactions
with peers, and opportunities for cognitively stimulating play, whereas
poor-quality care was conceptualized as involving negative interactions
with caregivers and peers and aimless wandering. From these and other
studies during this period, process quality came to refer to the experi-
ences that children have with caregivers, peers, and materials.
Further progress in addressing the quality question occurred with
the development and adoption of a common set of measures of pro-
cess quality. The Early Care Environment Rating Scale (ECERS;
Harms & Clifford, 1980) consists of 7-point ratings of the social, lan-
guage, reasoning, and physical environment in child care centers. The
Infant/Toddler Environment Rating Scale (ITERS; Harms, Cryer, &
Clifford, 1990) and the Family Day Care Rating Scale (FDCRS;
Harms & Clifford, 1989) are related measures of center-based care for
children less than 2 1/2 years and child care homes, respectively. The
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392 Merrill-Palmer Quarterly
Observational Record of the Caregiving Environment (ORCE), devel-
oped by the SECC (NICHD ECCRN, 1996, 2000a) assesses quality in
all types of care using time-sampled behavioral counts of caregiver
actions, peer interactions, and child activities as well as qualitative rat-
ings of caregivers’ behaviors. Age-appropriate versions are available for
infants, toddlers, and preschoolers. Quality also is measured by struc-
tural/caregiver characteristics such as child-adult ratio and caregiver’s
training and education.
Motivated by the policy question of “How can process quality be
improved?” and the search for easy-to-monitor indicators, researchers
have considered relations between structural/caregiver characteristics
and process quality. From this work, consistent findings have emerged
(Committee on Family and Work Policies, 2003; Vandell & Wolfe,
2000). In settings in which child-adult ratios are lower, caregivers spend
less time managing children in their classrooms and children are less
apathetic and distressed (Ruopp et al., 1979); caregivers are more stim-
ulating, responsive, warm, and supportive (NICHD ECCRN, 1996,
2000a); and process quality scores are higher (NICHD ECCRN, 1996,
2000a; Phillips, Mekow, Scarr, McCartney, & Abbott-Shim, 2000).
The number of children in the group also is associated with process
quality. In multivariate analyses that controlled for child-adult ratio,
caregiver training, and caregiver education, the NICHD ECCRN
(1996, 2000a) found that caregivers were more responsive, socially
stimulating, and less restrictive when there were fewer children in the
group. Process quality also is higher in child care homes that are in
compliance with recommended age-weighted group sizes (Clarke-
Stewart, Vandell, Burchinal, O’Brien, & McCartney, 2002).
Caregivers’ education—both formal education and specialized train-
ing—also is related to process quality. Caregivers tend to be more stimu-
lating, warm, and supportive, to organize materials better, and to provide
more age-appropriate experiences when they have more formal education
and more child-related training (Burchinal, Cryer, Clifford, & Howes,
2002; Clarke-Stewart et al., 2002; NICHD ECCRN, 1996, 2000a; Phillips
et al., 2000). Two experimental studies—the National Child Care Study
(Ruopp et al., 1979) and the Florida Child Care Improvement Project
(Howes, 1997)—have provided evidence of causal relationships between
structural/caregiver characteristics and process quality.
Child Care Quality and Child Developmental Outcomes
The development of measures of child care quality paved the way
to examine the effects of quality on child developmental outcomes in a
series of three logically related propositions (NICHD ECCRN, 2000a).
The first proposition is that quality, measured by structural/caregiver
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Early Child Care 393
characteristics and process quality, is related to child functioning in the
child care setting. The second proposition is that child care quality is
related to (influences) children’s concurrent functioning in other set-
tings such as home or lab. And the third proposition is that child care
quality is related to (influences) children’s long-term child developmen-
tal outcomes. In the text that follows, research pertaining to each propo-
sition is presented.
Child Care Quality and Child Behavior in Child Care. A recent
review by the National Academy of Science (Committee on Family
and Work Policies, 2003) reported six studies as finding relations
between process quality and children’s behavior in the child care set-
ting, and six studies as finding relations between structural/caregiver
characteristics and child behavior in the child care setting. To summa-
rize these findings, children appeared happier and more securely
attached to caregivers in care settings in which process quality was
higher and adult-child ratios were lower. Children appeared more
prosocial and positively engaged with peers when caregivers were sensi-
tive and positive to them and when child-adult ratios were lower. Chil-
dren were rated as more cognitively competent during free play in child
care settings that offered more opportunities for art, blocks, and dra-
matic play, and in settings in which caregivers had college degrees and
more early childhood training.
Recent research also has related child care quality to physiological
measures (Dettling, Parker, Lane, Sebanc, & Gunnar, 2000). Children
who attended child care homes that were higher in quality showed
decreases in cortisol from morning to afternoon, whereas children who
attended poorer quality child care homes showed increases in cortisol
from morning to afternoon. This rise is the opposite pattern of the typ-
ical circadian rhythm of cortisol, but it is similar to a rise across the
work day that has been recorded in adult executives who were under
high pressure at work.
Thus, research suggests that children who attend higher quality
child care are exposed to different environments and hence engage in
different behaviors and activities than children who attend poorer
quality child care. The next question is whether variations in quality
are related to child functioning in other contexts.
Child Care Quality and Concurrent Cognitive and Social Develop-
ment. Twenty-three studies were cited by the National Academy’s
Committee on Family and Work Policies (2003) as finding relations
between process quality and children’s cognitive and socioemotional
development in other contexts, after controlling for family and child
background factors. In particular, the committee noted that children
whose care was higher in process quality scored higher on concurrently
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394 Merrill-Palmer Quarterly
administered language and cognitive tests, had fewer behavior prob-
lems, and were more socially competent. Since the report was prepared,
other investigators (Loeb, Fuller, Kagan, & Carrol, 2004; Love et al.,
2003) also have found higher quality care (measured by the ECERS
and FDCRS) to be associated with better cognitive performance and
fewer behavior problems.
The Committee on Family and Work Policies (2003) cited 14 stud-
ies in relation to structural/caregiver characteristics and child develop-
mental outcomes. For example, the NICHD ECCRN (1999b) found
positive developmental outcomes, controlling for maternal education
and parenting quality, when children attended centers that were in
compliance with the American Public Health Association’s recom-
mended structural and caregiver guidelines. Children who attended
centers that met child-adult ratio standards displayed fewer behavior
problems and more positive social behaviors according to their mothers
than children whose centers did not meet the recommended standard.
When centers met the recommended guidelines for staff specialized
training and education, children exhibited fewer behavior problems
and obtained higher school readiness and language comprehension
scores. In subsequent analyses at 4 1/2 years, larger group sizes were
associated with lower academic achievement and lower cognitive devel-
opment, and higher caregiver education was related to higher cognitive
development and higher academic achievement, controlling for family
factors and children’s prior cognitive functioning (NICHD ECCRN &
Duncan, 2003). Similar relations between structural/caregiver charac-
teristics and child developmental outcomes have been found in child
care homes (Clarke-Stewart et al., 2002).
Child developmental outcomes also have been examined in rela-
tion to aggregated structural/caregiver characteristics. Some programs,
for example, trade off teacher training and group size by having teach-
ers who have more training and education care for more children,
whereas other programs have highly trained teachers assigned to fewer
children. And in still other programs, centers fail to meet any recom-
mended standards. In the SECC (NICHD ECCRN, 1999b), children
who attended centers that met more recommended standards had
fewer behavior problems and higher school readiness and language
comprehension scores. In these analyses, for example, 3-year-olds who
attended centers that met none of the recommended guidelines scored
14 points below the mean of the norming sample for the Bracken Basic
Concept Scale, whereas 3-year-olds in centers that met all four stan-
dards scored 2 points above the mean of the norming sample, a
16-point difference.
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Early Child Care 395
The available experimental evidence indicates causal relations
between child care quality and child developmental outcomes. In the
National Day Care Study (Ruopp et al., 1979), preschoolers who were
assigned to classrooms in which teachers had more education and train-
ing displayed greater gains in cooperative behavior, task persistence, and
school readiness over a 9-month period relative to children assigned to
classrooms in which teachers had less education and training.
Child Care Quality and Longer-term Outcomes. Eighteen studies
cited by the Committee on Family and Work Policies (2003) examined
relations between child care quality and children’s subsequent develop-
ment. Relations were more evident in studies that had assessed quality
at several points in time (Burchinal et al., 2000; NICHD ECCRN,
2000b, 2002b) and less evident in studies that relied on a single assess-
ment (Chin-Quee & Scarr, 1994; Deater-Deckard, Pinkerton, & Scarr,
1996). These discrepancies may be explained by the reliability of the
child care scores. Because children often experience several care
arrangements, longitudinal assessments of quality probably yielded
more accurate indications of quality.
In the SECC (NICHD ECCRN, 2000b, 2002b; 2003b), cumulative
measures of caregiver behavior as measured by the ORCE predicted
children’s performance on standardized cognitive and language assess-
ments at 15, 24, 36, and 54 months, controlling for amount and type of
care and an extensive list of family covariates. In the Cost, Quality, and
Outcomes Study, a prospective longitudinal study of 579 children who
attended 151 centers, process quality as measured by the ECERS predicted
cognitive, language, and social development during the early gradeschool
years (Peisner-Feinberg et al., 2001). Children who had closer relationships
with their preschool teachers were more sociable in kindergarten, control-
ling for prior child adjustment and family factors, and children who were
enrolled in higher quality child care displayed better math skills prior to
school entry and during kindergarten and 2nd grade. In other analyses
from the Cost, Quality, and Outcome Study, children who had closer rela-
tionships with their caregivers at age 4 years were reported by their 2nd-
grade teachers to be more socially competent with peers, controlling for
family factors and prior child functioning (Howes, 2000).
Relations between structural/caregiver characteristics and children’s
subsequent social and cognitive development also have been reported.
Howes (1988), for example, found relations between structural/caregiver
characteristics (teacher training, child-adult ratio, group size, a planned
curriculum, and space) at age 3 years and children’s functioning in 1st
grade. Children whose early care met more structural/caregiver guide-
lines had fewer behavior problems and better work habits in comparison
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396 Merrill-Palmer Quarterly
to children whose early care met fewer guidelines, controlling for family
factors. In a different sample, children were rated as more difficult by
preschool teachers and as more hostile by kindergarten teachers when
they had a history of poor-quality care, as measured by a composite
score of structural/caregiver characteristics (child-adult ratio, caregiver
training, caregiver stability) at 18, 24, 30, and 36 months (Howes, 1990).
Thus, the available evidence indicates that child care quality is
related to child developmental outcomes during the early elementary
school years. We do not know if these early relations are maintained
after this period, if they disappear, or if the early relations are magni-
fied over time.
How Large Are the Effects of Quality?
In addition to considering statistical significance, it is informative
to consider the practical significance of effects (McCartney & Rosen-
thal, 2000). One way of evaluating practical significance is to compare
the size of an obtained effect to other effects such as parenting and
poverty that are believed to be important. In the case of cognitive func-
tioning, effect sizes (d) associated with child care quality in the SECC
were .39 for school readiness and .44 for expressive language at 36
months, whereas effect sizes for parenting and home quality were
roughly twice as large, .83 and 1.01, respectively (NICHD ECCRN,
1999c). For children’s preacademic skills at 54 months, the effect size
(d) of child care quality was .39, and the effect size of poverty was .83.
Thus, the child care effects were roughly half the size of parenting and
poverty. Against these benchmarks, one can conclude that effects asso-
ciated with child care quality are meaningful.
Are Quality Effects Moderated by Child and Family
Characteristics?
In addition to the main effects described above, investigators have
identified some instances of moderated effects. In some domains, poor-
quality care appears to function as a risk factor. For example, in the
SECC, low-quality care coupled with low maternal sensitivity was asso-
ciated with insecure infant-mother attachment relationships (NICHD
ECCRN, 1997b). In other cases, high-quality child care served as a pro-
tective factor for children who were otherwise at risk. Children in the
SECC whose mothers were depressed appeared more positively engaged
with their mothers at age 4 1/2 years and 1st grade when they attended
higher quality child care (NICHD ECCRN, 2003c). In analyses of
school readiness, receptive language, and expressive language, higher
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Early Child Care 397
quality child care was found to buffer young children from the negative
effects of family poverty (McCartney, Dearing, & Taylor, 2003).
Next Steps
The recent findings pertaining to the effects of child care quality
are consistent with Lamb’s summary conclusions in the 1998 Hand-
book of Child Psychology that (a) high-quality child care has positive
effects on intellectual, verbal, and cognitive development, and (b) chil-
dren receiving high-quality care have superior relationship skills
whereas children receiving poor-quality care have deficient skills. Fur-
thermore, evidence from multiple studies of relations between struc-
tural/caregiver characteristics and process quality provide guidance for
ways to support or improve quality.
At the same time, there are a number of unknowns with regard to
child care quality that warrant further study. First, researchers have
examined effects of quality only through the primary grades (kinder-
garten, 1st grade, and 2nd grade). We do not know if the effects associated
with quality are maintained through middle childhood and adolescence.
Second, we do not know how many children attend poor-quality child
care in the United States or elsewhere because only convenience sam-
ples have been studied. Quality estimates derived from the NICHD
SECC, however, suggest that child care quality is not high. Positive
caregiving was rated as “not characteristic” in fully 60% of the settings
that were observed, and only 10% of the settings were rated as excellent
(NICHD ECCRN, 2000a). Representative surveys of child care qual-
ity, conducted at regular intervals to assess quality trends over time, are
clearly needed.
In addition, we have not studied the effects of child care quality
beyond its impact on individual children. Studies of the aggregated
effects of child care quality on public school classrooms are needed to
ascertain if high-quality care serves as a springboard for classrooms to
function well or if poor-quality child care places classrooms at risk. It
seems likely that classrooms containing more children who had attended
high-quality child care will differ from classrooms containing a prepon-
derance of children who had attended poor-quality child care. Finally,
we do not know which sets of policies are the best ones to adopt if we
want to improve child care quality or to support high-quality child care.
A number of proposals (Blau, 2001; Helburn & Bergmann, 2002; Lom-
bardi, 2003; Vandell & Wolfe, 2000) have been put forward, but these
proposals have not been tested. Experimental studies are needed to test
the effectiveness of different approaches for improving child care quality
(both process quality and structural/caregiver characteristics) and to
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398 Merrill-Palmer Quarterly
relate these strategies to child developmental outcomes. Evaluations of
these alternative models will be strengthened by further collaboration of
scholars in psychology, education, economics, and public policy.
Do Amount and Timing of Early Child Care Matter?
Questions about the effects of amount and timing are also central
to child care research. Jay Belsky (1986, 1988, 2001) has played a cen-
tral role in framing these questions. Citing evidence of relations
between amount of early child care and children’s noncompliance and
aggression in the initial research (Baydar & Brooks-Gunn, 1991; Bates
et al., 1994; Schwarz, Strickland, & Krolick, 1974; Vandell & Corasan-
iti, 1990), Belsky argued that early and extensive hours place young
children at risk for socioemotional problems. Others, however, coun-
tered that these relations could be explained by (a) the quality of the
child care (Phillips, McCartney, Scarr, & Howes, 1987), (b) differences
in family background (Richters & Zahn-Waxler, 1990), or (c) a failure
to distinguish between avoidance and independence in assessments of
infant attachment relationships and between child assertiveness and
aggressiveness in assessments of older children (Clarke-Stewart, 1989).
Because the initial research investigating amount and timing of care
did not include measures of child care quality, assertion or indepen-
dence, and controlled for few family factors, it was not possible to test
these different possibilities. In recent years, however, researchers have
adopted more comprehensive study designs that enabled them to eval-
uate these alternative explanations. These findings are reviewed below.
Although researchers and policymakers are interested in under-
standing both the effects of amount of care and the effects of when
care was initiated, the reality of child care participation, at least in the
Unites States, makes it difficult to disentangle these effects. For exam-
ple, 84% of the children in the SECC experienced nonmaternal care on
a routine basis by 12 months (NICHD ECCRN, 1997a). Of this group,
72% entered care by 4 months. At first entry, infants were in care for 29
hours a week, on average. Furthermore, once care was initiated, the
amount of time spent in care on a weekly basis remained more or less
stable throughout early childhood. Thus, timing and amount of care
are highly correlated.
Investigators who have studied the effects of these naturally occur-
ring variations in amount and timing have approached the problem of
colinearity in two ways: (a) by focusing on either amount or timing in
their analyses but recognizing that some (most?) of the variance may
be shared with the omitted variable, and (b) by including both amount
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Early Child Care 399
and timing in their analyses and recognizing that focusing only on
unique variance may result in substantial underestimations of both
effects. In the text that follows, much of the evidence reflects the com-
bined effects of amount and timing.
Attachment Security
One of the central questions motivating child care research in the
1980s and 1990s was whether early and extensive child care increased
the likelihood of children developing insecure attachment relation-
ships with their mothers. In the initial studies (see Barglow, Vaughn, &
Molitor, 1987; Belsky & Rovine, 1988), elevated rates of insecure
attachment were reported in children who experienced extensive child
care during the first year. None of these studies, however, controlled
for child care quality, and most did not control for potential family
differences.
More recently, the SECC (NICHD ECCRN, 1997b) examined
relations between early and extensive child care and child attachment
at 15 months, controlling for quality and type of child care and for
family background, in a large sample of children (n= 1,153). The
strongest predictors of attachment security were mother’s observed
sensitivity with the child at 6 and 15 months, and the mother’s psycho-
logical adjustment. Amount of early child care was significant only in
conjunction with maternal sensitivity: the likelihood of an insecure
attachment increased only if children were in child care for more than
10 hours a week and mothers were highly insensitive. If mothers were
sensitive, being in care for more than 10 hours a week was not related
to attachment quality. A similar interaction was observed at 36 months
(n= 1,140) (NICHD ECCRN, 2001b): High hours were associated
with an ambivalent attachment only when mothers were insensitive.
Quality of Mother-Child Interaction
Researchers also have considered associations between the
amount of early child care and the quality of mother-child interac-
tion. Related studies considered the effects of early maternal employ-
ment. Some of these studies reported amount of early care to be
related to more negative mother-infant interactions (Campbell, Cohn,
& Meyers, 1995; Owen & Cox, 1988). Others have found positive
effects of amount of care on mother-child interaction (Crockenberg &
Litman, 1991; Vandell, 1979), and still others found no effects
(Burchinal, Bryant, Lee, & Ramey, 1992). Much of the initial research
in this area, like other research of the time, was limited because of
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400 Merrill-Palmer Quarterly
small sample sizes, few controls for family background, and a reliance
on a single time of measurement.
Recent reports have sought to address these limitations. In the
SECC, mother-child interactions were observed at 6, 15, 24, and 36
months for over 1000 families. More hours in child care was associated
with less maternal sensitivity and less child positive engagement with the
mother, controlling for quality and type of child care, family income,
maternal education, marital/partner status, maternal depressive symp-
toms, maternal separation anxiety, child gender, child temperament, and
ethnicity. The effect size of child care hours (.15) was similar to that of
maternal depression and difficult child temperament but considerably
smaller than the effect associated with maternal education (.70).
In a follow-up report (NICHD ECCRN, 2003c), the study of rela-
tions between amount of child care and mother-child interaction was
extended to age 4 1/2 years and 1st grade. At these later ages, relations
between hours and mother-child interaction were evident only for par-
ticular subsamples. Higher hours were associated with less maternal
sensitivity and less positive engagement in White children, but greater
maternal sensitivity and more positive engagement in African Ameri-
can and Hispanic children.
The Wisconsin Maternity Leave and Health Project (Clark, Hyde,
Essex, & Klein, 1997) contrasted the quality of mother-infant interac-
tion at 4 months in 198 families in which mothers had 6 weeks versus
12 weeks of parental leave. Shorter leaves were associated with mothers
expressing more negative affect and negative behavior toward their
infants. In addition, mothers were less likely to express positive affect
to their infants when short leaves were combined with maternal depres-
sive symptoms and difficult child temperament.
Behavior Problems
Amount of child care also has been considered in relation to chil-
dren’s socioemotional adjustment (behavior problems and social com-
petence) in a series of reports in which child care quality and type were
controlled as well as family factors. At age 2 years, children who had
spent more hours in child care were observed to have more negative
interactions with peers (NICHD ECCRN, 2001a) and were reported
by their caregivers to have more behavior problems and by their moth-
ers to be less socially competent than children who had fewer hours in
child care (NICHD ECCRN, 1998). At age 4 1/2 years, children who
had been in child care for more hours were observed to have more neg-
ative play with a friend and were reported by caregivers to be less
socially competent, and to have more externalizing behavior problems
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Early Child Care 401
and more conflicts with caregivers (NICHD ECCRN, 2003a). In
kindergarten, children with more hours in early child care were
reported by mothers and teachers to have more externalizing behavior
problems, and teachers reported more teacher-child conflict.
Several alternative explanations for these findings have been exam-
ined (NICHD ECCRN, 2003a). One possibility is that the relations
were the result of other aspects of child care. Another possibility is
that the hours effects were mediated by differences in mother-child
interaction. These possibilities were tested in analyses that included
controls for other aspects of child care (quality, type, instability, expo-
sure to peers) and maternal sensitivity. The addition of these controls
resulted in modest reductions in the hours coefficients, but the coeffi-
cients continued to be statistically significant, indicating that the hours
findings were not explained by quality of child care or quality of par-
enting, at least as they were measured in this study.
Studies by Gunnar and colleagues (Dettling, Gunnar, & Donzella,
1999; Tout, de Haan, Campbell, & Gunnar, 1998; Watamura, Donzella,
Alwin, & Gunnar, 2003) suggest a potentially fruitful avenue for under-
standing the relations between hours in care and adjustment. These
investigators examined children’s cortisol levels and patterns at child
care and at home. Salivary cortisol was observed to increase from
midmorning to midafternoon on those days in which children were in
centers but not on days in which these same children were at home
(Watamura et al., 2003). In other reports, the largest increases in cor-
tisol across the day were observed in children who had the most diffi-
culty regulating negative emotions and behavior (Dettling et al., 1999),
were more fearful (Watamura et al., 2003), were less involved in peer
play (Watamura et al., 2003), and were less socially competent (Tout et
al., 1998). Rises also were more evident in toddlers and preschoolers
than in infants and school-aged children (Dettling et al., 1999; Wata-
mura et al., 2003). These findings suggest that toddlers and preschoolers
who are learning to negotiate with peers may experience group settings
as socially demanding and stressful. What is not known is whether
changes in the organization of child care programs or in caregivers’
efforts might result in less stressful and more supportive social environ-
ments for children (Maccoby & Lewis, 2003).
How Large Are the Quantity Effects on Child Behavior
Problems?
The practical significance of the quantity findings can be evalu-
ated in several ways. In terms of effect sizes, the effect sizes associated
with amount of early care and behavior problems ranged from .08 to
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402 Merrill-Palmer Quarterly
.20 in the SECC. Effect sizes for parenting quality were similar, ranging
from .09 to .16. This comparison suggests that the quantity effects are
meaningful.
A second way of evaluating the significance of the behavior prob-
lems findings is to compare the scores in the SECC to those of the sam-
ple used to norm the Child Behavior Checklist (CBCL). In the SECC,
children who were in care for less than 30 hours a week received scores,
on average, that were less than the norming sample mean of 50: chil-
dren who were in child care for 0 to 9 hours a week scored, on average,
47.8 and children in care for 10 to 29 hours a week scored 49.0. Chil-
dren who averaged more than 30 hours a week of child care from 3 to
54 months scored higher, on average, than the norming sample mean of
50. Children who averaged 30 to 45 hours a week received scores of
51.3 on average. Children in child care more than 45 hours a week from
3 to 54 months had the highest externalizing scores (53.1 at 54 months
and 52.1 at kindergarten), a difference of about one third of a standard
deviation above the norm.
A third way of assessing the size of the quantity effect is to con-
sider the proportion of children evincing “high” behavior problems,
defined as 1 standard deviation above the mean for the CBCL norming
sample. With this criterion, one would, by definition, expect 17% of
the children to score 60 or higher. In the SECC, only the group of chil-
dren who averaged more than 45 hours per week in child care from 3 to
54 months exceeded this expectation—24% were reported by teachers,
and 26% were reported by mothers, to display high levels of behavior
problems at 54 months. These analyses suggest that it was only chil-
dren who spend substantial hours in child care (45 hours a week) over
an extended period (3–54 months) who displayed more externalizing
behavior problems than might be expected within the population as a
whole.
Cognitive and Language Development
Findings are mixed with respect to amount (and timing) of child
care and children’s cognitive, language, and academic performance.
Analyses conducted by the NICHD ECCRN (2000b, 2002b, NICHD/
ECCRN & Duncan, 2003) found no relations between amount/timing
and cognitive and language measures at 15, 24, 36, or 54 months, con-
trolling for other aspects of care and family factors. Others (Baydar &
Brooks-Gunn, 1991; Brooks-Gunn et al., 2002; Waldfogel, Han, &
Brooks-Gunn, 2002), however, have detected amount/timing effects
under some conditions. In analyses of the European American children
in the SECC, Brooks-Gunn et al. (2002) reported that children whose
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Early Child Care 403
mothers were employed for 30 or more hours a week by 9 months had
poorer preacademic skills at 36 months than children whose mothers
worked less than 30 hours a week. These effects were not evident in the
European American children’s cognitive performance prior to 36
months nor in the cognitive performance of ethnic minority children at
15, 24, or 36 months. These researchers also have found extensive
maternal employment in the first year to be related to lower cognitive
performance of European American (but not African American and
Hispanic) participants in National Longitudinal Survey of Youth
(Baydar & Brooks-Gunn, 1991; Waldfogel et al., 2002). Vandell and
Ramanan (1992), in contrast, found early maternal employment to be
positively associated with academic performance in grade 2 for the
subsample of low-income children in the National Longitudinal Sur-
vey of Youth.
Next Steps
Additional research is needed to identify the processes that medi-
ate relations between quantity of care and child developmental out-
comes. By and large, in the work to date from the SECC, effects were
not attenuated when maternal sensitivity and child care quality were
included as controls, suggesting that the quantity effects were not
mediated by the quality of caregiving provided by child care providers
or mothers, at least as measured by the study investigators.
An important next step is to consider other aspects of child care
quality. The quality of the peer environment is particularly impor-
tant to consider (Fabes, Hanish, & Martin, 2003; Watamura et al.,
2003). The specific strategies that caregivers use to promote chil-
dren’s social skills and to handle children’s noncompliance and
aggression also may help to explain the effects associated with quan-
tity of care. The extensive child care observations conducted in the
SECC, which are available in the public release data set, include peer-
related items as well as observations of caregivers’ socialization
strategies. These observations could be useful in testing these media-
tion hypotheses.
Further research also is needed to disentangle the effects of
amount and of timing. One possibility, if sufficient families are inter-
ested, is to mount an experimental study of paid parental leave in
which children (and families) are assigned to varying amounts of
child care (0–40 hours) and to different entry ages (2–24 months).
Recent large-scale experimental studies of early education and work-
based antipoverty programs indicate that such projects are feasible and
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404 Merrill-Palmer Quarterly
compelling (Administration for Children and Families, 2002; Gennet-
ian & Miller, 2002; Huston et al., 2001).
Does Type of Child Care Matter?
A third question central to child care research is whether child
developmental outcomes are affected by different types of child care. In
some cases, correlational designs have related attendance at centers,
child care homes, and relative care to child developmental outcomes.
Others have used experimental and quasi-experimental designs to study
the effects of participation in high-quality early education programs.
In an early study of 80 preschool-aged children in Chicago,
Clarke-Stewart (1987) found child care centers, child care homes, and
in-home care (nannies and relatives) to differ in a myriad of ways.
Child care centers typically had more highly educated caregivers, larger
group sizes, more time spent in “lessons,” more structured activities,
and more child-oriented materials, activities, and toys. Caregivers in
centers had more professional orientations and were less likely to pro-
vide care as a favor for the family. In contrast, child care homes typi-
cally devoted more time to free exploration, casual learning, and
watching TV than did centers. Consistent with their more educational
focus, children who attended centers scored higher on standardized
cognitive assessments, controlling for family demographic characteris-
tics and observed parenting. Children in center-based care also were
more competent with strangers and independent of mothers in a labo-
ratory playroom. Least advanced were children with caregivers in their
own homes.
Similar findings were obtained in the SECC (NICHD ECCRN
1996, 2000a). Centers had the largest group sizes, the highest child-
adult ratios, the most stimulating physical environments, and caregivers
with the most training and education. Child care homes (sometimes
called family day care) were intermediate between centers and the care
provided by grandparents and nannies. Child developmental outcomes
were related to type of care. Children who had more experience in
center-based care (defined as the proportion of 3-month epochs that
they had attended centers) obtained higher cognitive and language
scores at ages 2 years (2000b), 3 years (2000b), and 4 1/2 years (2002b),
controlling for family background characteristics and the quality and
amount of child care. Effect sizes in these analyses ranged from .21 to
.43. In other analyses, changes in cognitive functioning associated with
center care were considered: children who attended centers between the
ages of 27 and 54 months (but not earlier) scored 4.1 points higher on
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Early Child Care 405
cognitive tests relative to children who never attended centers during
this period, controlling for family characteristics (effect size = .27)
(NICHD ECCRN & Duncan, 2003).
Loeb et al. (2004) also determined center-type care to be related
to cognitive benefits. In that study, children in three sites (n= 451)
were observed in centers, kith and kin, and child care homes after
their parents began working in connection with TANF (Temporary
Assistance to Needy Families). Children were 2 1/2 years on average at
Wave 1, and 4 years on average at Wave 2. Children who attended cen-
ters during both waves and children who moved to centers by Wave 2
obtained higher cognitive and school readiness scores (effect sizes 0.6
and 0.4), controlling for family background and prior child perfor-
mance. Participation in centers was not related to child behavior
problems.
The available experimental and quasi-experimental evidence indi-
cates that high-quality center-based care confers cognitive and academic
benefits for children who are at risk for school failure. In the Carolina
Abecedarian Project, the treatment group attended a high-quality full-
day program from shortly after birth through age 5 years while the con-
trol group received family support social services, pediatric care, and
child nutritional services. At 8 and 12 years, the treatment group
obtained higher IQ scores (Campbell & Ramey, 1994). At age 15 years,
they had higher reading and mathematics achievement scores, were less
likely to have been retained a grade, and were less likely to have been
placed in special education (Ramey, Campbell, & Blair, 1998). At age
21 years, they were more likely to have attended a 4-year college (Camp-
bell, Ramey, Pungello, Sparling, & Miller-Johnson, 2002). Not all of
the effects reported from this program were positive, however. In grade
1, children in the treatment group were reported by teachers to be more
aggressive (Haskins, 1985).
A second experimental study, the Perry Preschool Project, also
found long-term effects of participation in a high-quality center-based
program, in this case a half-day program that began at age 3 years. This
sample of 123 children has been followed to 27 years, at which time
members of the experimental group had higher incomes and fewer
arrests, and were less likely to be receiving public assistance, than mem-
bers of the control group (Schweinhart, Barnes, & Weikart, 1993).
A third experimental study, the Infant Health and Development
Project, was a multisite randomized treatment study that included
high-quality center-based care as a component of a comprehensive
intervention targeted to low-birth-weight (LBW) premature infants.
The treatment group received home visits from the 1st through the 3rd
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406 Merrill-Palmer Quarterly
year and high-quality, full-day center-based programming during their
2nd and 3rd years. Children’s cognitive and behavioral functioning was
assessed at ages 5 and 8 years (Brooks-Gunn et al., 1994). The initial
analyses contrasting the intention-to-treat group versus the control
group found cognitive benefits at ages 5 and 8 years only for the heav-
ier LBW infants. A recent paper (Hill, Brooks-Gunn, & Waldfogel,
2003) has extended this study to consider dosage. The dosage analyses
indicated considerably larger cognitive effects through age 8 years for
both lighter and heavier LBW infants who had attended the program
for more days.
Results from quasi-experimental studies also support the proposi-
tion that high-quality center-based programs can have long-term bene-
ficial effects for low-income children. In a series of papers (Reynolds,
1994; Reynolds & Robertson, 2003; Reynolds & Temple, 1998;
Reynolds, Temple, Robertson, & Mann, 2001), Reynolds and colleagues
have followed the educational and social development of African
American and Hispanic children who lived in central city Chicago. The
treatment group consisted of children who participated in government-
funded Title I early childhood programs in 1985–1986 (n= 989); the
comparison group consisted of other children in the same neighbor-
hoods who did not attend these programs and received the “treatment
as usual” in the community (n= 550). The Chicago Parent-Child Center
curriculum emphasized basic skills in language and math through fairly
structured activities that were taught by teachers with college degrees;
parent involvement was an integral part of the program.
Program effects have been found through age 20. Children who
participated in the early childhood program obtained significantly
higher math and reading achievement test scores at 5, 8, and 14 years,
controlling for family risk status, child gender, and program participa-
tion during the primary grades (Reynolds & Temple, 1998). At age 20,
participants were more likely to have completed high school and to
have low rates of juvenile crime (Reynolds et al., 2001). Program par-
ticipation also was associated with reductions in child abuse and child
neglect, with the largest effects seen when children were 10 to 17 years
old (Reynolds & Robertson, 2003).
Conclusions
The last 25 years have been marked by substantial progress in
answering questions about the effects of child care quality, amount and
timing, and type. This progress has occurred, in part, because of the
study of large and diverse samples, the development of a common set
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Early Child Care 407
of reliable and valid measures that facilitated cross-study comparisons,
the use of sophisticated analytic strategies that minimized the likeli-
hood of biased findings, longitudinal designs in which child care and
the family were assessed at regular intervals, and the consideration of a
broad array of social and cognitive outcomes evaluated by multiple
methods.
With respect to child care quality, both process quality (the experi-
ences that children have with caregivers, peers, and materials) and
structural/caregiver features have been consistently found to predict
children’s cognitive, language, and social development, even when
extensive covariates are included in analyses. Much of this research has
reported main effects of quality, but there is some evidence that the
effects of child care quality are larger in children who are at risk
because of poverty, maternal depression, or poor parenting. Effects
associated with child care quality are “small” or “moderate” by
Cohen’s (1988) standard, but they may still be judged as meaningful
when compared to the effects of poverty and parenting.
With respect to amount and timing of child care, the research evi-
dence suggests that substantial hours in care beginning in infancy is
associated with less sensitive mother-child interactions and with more
behavior problems in children. In the NICHD SECC, children in child
care for less than 30 hours a week from 3 to 54 months had externalizing
scores that were, on average, below the norming sample mean of 50,
whereas children in child care for substantial hours (i.e, more than 45
hours a week from 3–54 months) had externalizing scores that were, on
average, 2 to 3 points above the norming sample mean. Children with
substantial early hours also evinced a higher than expected rate of
“high” levels of behavior problems, while children with less extensive
hours did not. Further research is needed to identify the processes that
mediate and moderate relations between amount of care and behavior
problems.
Finally, with respect to the effects of different types of care, exper-
imental studies of high-quality programs serving at-risk children have
found positive short-term and long-term effects on children’s aca-
demic, cognitive, and social outcomes. Correlational studies also indi-
cate that attending child care centers is associated with higher cognitive
and language scores.
Although much progress has been made in understanding the
effects of early child care further research is clearly needed because
there is much we still do not know. Our unanswered questions include
the following: First, will effects of child care quality, amount, and type
continue to be evident during middle childhood and adolescence? That
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408 Merrill-Palmer Quarterly
is, are the effects of early experience maintained or do they dissipate?
Second, what is the quality of child care in the United States? How
much of the available care is of poor quality? Third, do measures of
quality need to be expanded to reflect the peer context? Fourth, can
effective policies be implemented to improve child care quality? Fifth,
can the effects of amount and timing of early child care be disentan-
gled? Finally, what are the effects of different parental leave policies on
the well-being and development of children and families? As progress
is made on these questions, child care research should help to advance
developmental theory and application.
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