The purpose of this study is to investigate to what extent mathematics teachers teaching at secondary school 6, 7, and 8th grade students teach based on students' learning styles and to reveal how effective matching teachers' teaching styles with learners' learning styles in students' achievements is. As this research aims to reveal the case as it is, survey model was used in this study. This study was conducted on 700 secondary school students and 31 teachers who were teaching those students. The study was conducted in 2014-2015 education term at 9 schools which were randomly chosen from Balikesir Province Center. The data of the study was gathered from 31 secondary school mathematics teachers and 700 secondary school with the help of learning and teaching styles inventory scale. The results of this study reveal that teachers design the learning environments depending on their own learning styles and that there has been a close relationship between teachers' learning styles, students' learning styles and students' achievements in mathematics classes, that students' achievements increase when teaching is done based on their learning styles.