This article is situated within a theoretical framework, instructional congruence, articulating issues of student diversity with the demands of academic disciplines. In the context of a large-scale study targeting elementary school science, the article describes a research instrument that aims to combine the strengths of both quantitative and qualitative approaches to classroom data. The project-developed classroom observation guideline is a series of detailed scales that produce numerical ratings based on qualitative observations of different aspects of classroom practice. The article's objectives are both pedagogical and methodological, reflecting the dual functionality of the instrument: (a) to concretize theoretical constructs articulating academic disciplines with student diversity in ways that are useful for rethinking classroom practice; and (b) to take advantage of the strengths of qualitative educational research, but within a quantitative analytical framework that may be applied across large numbers of classrooms. © 2006 Wiley Periodicals, Inc. J Res Sci Teach 44: 424–447, 2007