In the climate of standards-based instruction and accountability, scaling up educational innovations is necessary to bring about system-wide improvements. As a result of fundamental tensions involving effective educational policies and practices for diverse student groups, scaling up is especially challenging in multilingual, multicultural, and inner-city settings. In this article, grounded in the instructional congruence framework, the authors highlight the challenges facing schools and teachers in articulating science disciplines with nonmainstream students' linguistic and cultural experiences while also promoting English language and literacy. Rigorous attention to such challenges is needed to make scaling up of educational interventions more effective and to answer the question of what constitutes "best policies and practices" for diverse student groups. (Contains 1 figure and 2 notes.)