This study investigated how Turkish mathematics teachers evaluate the effectiveness of classroom teaching in terms of improving students' mathematical proficiency. To this purpose, teachers were asked to evaluate a mathematics lesson as presented them in a vignette. By means of cluster analysis, the participants' evaluations of the lesson were described in five thematic dimensions, which could be further assembled into two overriding categories: students' understanding of the subject, and teachers' classroom practices. The overall aim of the current paper is to propose a preliminary model of the framework that Turkish mathematics teachers use to evaluate a mathematics lesson.