Much research has focused on student views about physics concepts, with an emphasis on the identification of alternative conceptions, and how curricula and professional development may ameliorate the situation. However, there has been little work on determining the extent of, and in separating, the student and teacher/classroom level variables that may impact student physics achievement. This study examined the effect of different student and teacher/classroom level variables on student understanding of physics concepts using hierarchical linear modeling (HLM), a regression based technique. The data were collected from 68 different teachers and 3,119 students who were using a reform curriculum, Active Physics. Teachers and students completed surveys asking about their beliefs, their classes and their personal characteristics. Students also completed a physics achievement test. The data show that students of teachers who used Active Physics for a greater portion of the year scored higher on the achievement test than did students of teachers who did not use the curriculum as much. Furthermore, the data show that the achievement gap was narrowed between boys and girls and between students with different attitudes toward physics. Additionally teachers who received inservice instruction on how to implement Active Physics narrowed the gap between students with different views of their classroom involvement. (Contains 2 tables and 2 figures.)