In the context of an experimental trial, the authors examined variability in treatment and control teachers' use of several "Responsive Classroom" (RC) practices to predict students' 4th grade academic achievement. Further, they examined the extent to which use of the "RC" practices is differentially important for subgroups of students. They conducted analyses corresponding to two research questions. First what is the relative contribution of practice-specific indices of teachers' use of "RC" practices on 4th grade students' mathematics and reading achievement? Second, to what extent are these associations moderated by student characteristics including initial achievement and gender? (Contains 2 tables and 2 figures.)