The purpose of this study is to examine the effect of teacher expectancy on student performance. The question is asked: Do teachers in secondary grades treat students for whom they have low expectations in ways that tend to fulfill them, and if so, what is the nature of this differential treatment? Differential teacher behavior (quantitative and qualitative differences in teacher-student interaction) was examined in four seventh-grade classrooms. Participating teachers were asked to rank the students in their class in order of their achievement. Students were ranked as high, middle, or low achievers. The ratings were used as the measure of teachers' expectations for classroom performance of the students. Overall results indicated that there were differences in the interaction of teachers with students at the various achievement levels. Comparison of high, middle, and low expectancy groups revealed quantitative differences in teacher-student contact but little difference in the quality of interaction patterns. The most notable finding of this study was that low achievement students received much less teacher contact than did the high and middle achievers. The results of this study provide support for the hypotheses that with grade level increase, qualitative differences in teacher-student interaction diminish, while quantitative differences may become more sensitive indicants of differential teacher behavior. (JD)