The first challenge of accomplishing the goals of any successful instruc-tional system depends on accurately assessing learners and leveraging the information to improve learning (e.g., Conati, 2002; Park & Lee, 2003; Shute, Lajoie, & Gluck, 2000; Snow, 1994). This paper describes an app-roach for modeling key competencies and developing valid assessments embedded within an immersive game. Specifically, we describe theoretical-ly-based research relating to stealth assessment, diagnosis, and instructional decisions, operational within an immersive game environment. Stealth assessment and diagnosis occur during the learning (playing) process, and instructional decisions are based on inferences of learners' current and pro-jected competency states. Can games be used to support meaningful learning? Most likely the answer is yes, conditional on more research being conducted in this area. In general, we believe that (a) learning is at its best when it is active, goal-oriented, contextual-ized, and interesting (e.g., Bransford, Brown, & Cocking, 2000; Bruner, 1961; Quinn, 2005; Vygotsky, 1978); and (b) learning environments should thus be interactive, provide ongoing feedback, grab and sustain attention, and have appro-priate and adaptive levels of challenge—i.e., the features of good games (e.g., Prensky, 2001; Salen & Zimmerman, 2004).