Multilevel modeling techniques were used with a sample of 643 students enrolled in 37 secondary school classrooms to predict future student achievement (controlling for baseline achievement) from observed teacher interactions with students in the classroom, coded using the Classroom Assessment Scoring System--Secondary. After accounting for prior year test performance, qualities of teacher interactions with students predicted student performance on end-of-year standardized achievement tests. Classrooms characterized by a positive emotional climate, with sensitivity to adolescent needs and perspectives, use of diverse and engaging instructional learning formats, and a focus on analysis and problem solving were associated with higher levels of student achievement. Effects of higher quality teacher-student interactions were greatest in classrooms with fewer students. Implications for teacher performance assessment and teacher effects on achievement are discussed. (Contains 2 figures and 5 tables.)