Thirteen of the 41 classroom observation dimensions derived from Medley's review of teacher effectiveness reports were scored on the Georgia Assessment of Teacher Effectiveness. Subjects were 53 fifth and sixth grade teachers in language arts and mathematics. The dimensions were: large group instruction; group size without adult supervision; student seatwork, teacher structuring, student choice; structured academic time; student verbal interaction; correct substantive responses to teacher questions; low cognitive level questions; teacher discusses student response; teacher hostility and rebuking behavior; disruptive student behavior; student time on task; non-substantive teacher-student interaction; and structured student behavior. The contribution of each dimension to spring-term student achievement on the Iowa Tests of Basic Skills (ITBS) was calculated, after eliminating variance attributed to the fall-term pretest, grade level, and socioeconomic status. All dimensions were significantly related to at least one of five ITBS subtests: vocabulary, reading, spelling, mathematics concepts, or mathematics problems. (CP)