In this study reciprocal peer tutoring was implemented in middle school mathematics classes for a six-month period. The effects of this methodology on students' mathematics achievements, mathematics anxiety levels, attitudes towards mathematics, and mathematics self-concepts were examined. Study participants included 768 students in grades 7-9 (12-15 years old). Statistically significant differences and positive effect sizes were reported for mathematics achievement, mathematics anxiety level, and mathematics self-concept (Hedge's g average value of 0.28). No significant statistical differences were reported for mathematics attitude. Students' repeating condition acted as significant moderators for mathematics anxiety. The main conclusion is that reciprocal peer tutoring can be very beneficial academically and psychologically for middle school mathematics students.