This quasi-experimental study examines the effects on student performance of a Javits-funded curriculum designed to respond to the needs of high-ability students in elementary and middle school social studies. The curriculum, implemented with all students in heterogeneous classrooms, addresses state standards while integrating advanced content, higher level process emphases, and a conceptual orientation. Data collection focuses on student performance in conceptual reasoning, critical thinking, and content learning and on teacher demonstration of specific desired teaching behaviors. Results demonstrate significant and important differences between treatment and comparison groups in the area of content learning, favoring the treatment group; no significant differences are found for the small subsample of gifted students. Subanalyses yield differential results for specific units and schools, potentially indicating issues of treatment fidelity. Contextual challenges and implications of the study are discussed, including issues related to social studies curriculum implementation and differentiation in the current standards-based environment. (Contains 7 tables and 1 note.)