This paper assesses the extent to which teachers’ actions in the classroom influence the school environment. The assessment is based on a statistical analysis of videotaped classroom observations of 51,329 teachers. The classroom environment was found to have a significant influence on students’ performance. More specifically, the teacher’s ability to handle the class as a group is consistently more significant than other measures of class environment. It was also founds that the overall school environment is a better predictor of students’ test results than the environment in the classrooms of the students whose test results are being reported. This suggests that the most effective course of action would be to improve the overall school environment, although individual teachers have less control over this factor.