The stability of teacher behavior has been one of the most important areas of process-product research. This study was designed to investigate teacher stability in the context of math instruction across classes and times of observation in order to assess the relationship between teaching styles and student learning outcomes. Specifically the study examines: the setting, purpose, and nature of the classroom interactions of a group of middle school mathematics teachers; the stability of mathematics teachers' instructions across classes and time of observations; and the consistency of teacher instruction over a period of time. Subjects (N=62) were mathematics teachers from 5 middle schools in a metropolitan school district in the Central South who taught at a single grade level (grade 6, 7, or 8) during the observed school year. Data were collected through use of the Teacher Roles Observation Schedule (TROS) which documents observed teacher behaviors in the context of ongoing classroom instructional-learning processes. Results offer the following insights into the classroom process: (1) interactions with students were mostly instructional, sometimes managerial; (2) explaining, questioning, and commenting to the whole class were frequently utilized; (3) the task's process was emphasized more than the product; and (4) classrooms became more active over time as teachers and students came to know each other better. It was also found that teacher stability decreased over the long term, and that teachers directed classroom instruction with considerable flexibility. (LL)