Microteaching is a teacher education technique whose contributions to pre-service teacher education are significant. Through this technique, pre-service teachers can find an opportunity to transform their subject matter knowledge and pedagogical content knowledge into practice. They see and improve their weaknesses of teaching skills such as lesson planning, organization of group work, classroom management, etc. The aim of this study was to investigate the effectiveness of microteaching in mathematics of primary pre-service teachers by using a quantitative approach. The research group involved 131 third grade pre-service teachers from the department of primary school education. In their course entitled "mathematics teaching II", the pre-service teachers lectured mathematics by using microteaching method for only once in a period of 40 minutes. To collect data, a 5-point Likert-type microteaching evaluation form was administered to the pre-service teachers. The exploratory factor analysis was performed. We found seven factors which explain the pre-service teachers' effectiveness in microteaching. The main results of the study indicate that the pre-service teachers had some problems in assessment, organization of group studies, and incorporating students' interest into teaching.