The aim of this study is to investigate the effects of reflective thinking-based teaching activities on academic achievement, retention and attitude towards English course in secondary school English classes. The research was carried out with pre-test-post-test design with experimental-control groups. The study was carried out in a private secondary school for 8 weeks in Konya, in 2016-2017 academic year. The study included a total of 35 students in the fifth grade, which included 18 students in the experimental group and 17 in the control group. In the experimental group, reflective teaching activities were used and in the control group the activities on the teacher's guide book based on the current curriculum were used. There was a significant difference between the post-test and retention scores of the experimental and control groups. However, experimental teaching practices did not lead to a significant difference in students' attitudes towards the course. It was found that reflective teaching practices had an impact on students' success and retention in secondary school English lessons.