The purpose of this study was to determine how the adoption of cooperative learning as an instructional strategy for teaching Integrated Science influences students' achievement and attitude towards studies. The study also determined how moderating variables like sex and ability affect students' achievement in Integrated Science when cooperative learning is used as an instructional strategy. To guide this study, five hypotheses were stated and tested at 0.05 level of significance. The design of the study was a 2x2x2x2 factorial, pre-test, post-test control group design. These included two instructional groups (cooperative and traditional classroom groups), sex (male and female), ability (high and low), and repeated testing (pre-test and post-test). The population of study was made up of 205 JS III students from where a sample of 120 students was randomly selected. The instruments used for the collection of data included: a Scholastic Ability Test in Integrated Science (SATIS), Students' Attitude Scale (SAS), and Integrated Science Achievement Test (ISAT). All the data collected were analyzed with analysis of co-variance statistic. The major findings of the study included: a significant higher achievement test scores of students in cooperative learning group than those in traditional classroom; a significant higher attitude scores of students in cooperative learning group than those in traditional classroom; a significant higher achievement test scores of all students of varying abilities in cooperative learning group than those in traditional classroom; a non-significant difference in achievement test scores between the male and female students in the cooperative learning group, and non-significant interaction effect between sex and ability, sex and method, ability and method and among method, sex and ability on achievement.