Using a series of regression equations, classroom process and student achievement data from 136 junior high school mathematics and English classes were analyzed to answer the following questions: (1) Are the classroom behaviors and achievement levels of students systematically different across classes of higher and lower ability? (2) Within classes, are the behaviors of higher and lower ability students systematically different? and (3) Does student ability level interact with the ability level of the class to affect systematically students' classroom behavior and achievement? Results of class level analyses suggest that better learning environments are associated with classes of higher mean ability, and that both higher ability students and lower ability students achieve better in higher ability classes. Interactions obtained between class and student ability levels suggest that differences in class environment associated with class ability level have more impact on achievement and behavior of lower ability students than on high ability students. Lower ability students appear to be more reactive to or dependent on class norms than are higher ability students. (Author)