This paper reviews significant research findings from the past 10 years which demonstrate that teachers' attitudes, expectations, and behavior have significant practical effects on student achievement. Although causes of differential interaction are not definitely established, it is clear that many teachers vary sharply in their interaction patterns with high- and low-achieving students. Explanations for this differential teacher behavior include the complexity of the classroom setting; the ambiguous nature of student performance, teachers' beliefs about causality (their ability to cause or to influence student performance); and the feedback pattern of expectation, interpretation, and student behavior. Recent research also suggests that variations in different teachers' behavior toward low-achieving students may encourage student passivity as a consequence of role confusion. There is also evidence that students may be adversely affected by grouping according to ability, which often results in social contexts not conducive to learning. Research on the influence of student behavior, perceptions, and self-perceptions of classroom learning is also reviewed. The way students interpret teachers' behavior, their own ability, and learning activities may have effects on classroom learning that are quite independent of teachers' actual intentions or perceptions. (TE)