In the current research climate favoring rigorous experimental studies of instructional scripts using randomly chosen treatment and control groups, education and literacy researchers and policy makers will do well to take stock of their current research base and assess critical issues in this new context. This review of research on classroom discourse as it affects reading comprehension begins by examining 150 years of research on classroom discourse, and then findings and insights shaped by intensive empirical studies of both discourse processes and reading comprehension over the last three decades. Recent sociocultural and dialogic research supports claims that classroom discourse, including small-group work and whole-class discussion, works as an epistemic environment (versus script) for literacy development. New studies examine situated classroom talk in relation to educational outcomes and cultural categories that transcend the classroom. (Contains 1 note.)