Peer tutoring in Mathematics has reported academic benefits across many educational levels, from Preschool to Higher Education. However, recent literature reviews and meta-analysis state that students experience higher gains in Primary or Elementary Education (ages 7-12 years) than in secondary education or middle school and high school (ages 13-18 years). This study examined the effects of peer tutoring on students' mathematics achievement in primary and secondary education under similar settings. 89 students from first, fourth, seventh, and ninth grades participated in the study. The design of this research was quasi-experimental with pretest-posttest without control group. The statistical analysis reported significant improvements for both, Primary and Secondary Education. The comparison between these educational levels showed that there were no significant differences in the increments of the students' marks. The global effect size reported for the experience was Cohen's d = 0.78. The main conclusion is that Peer Tutoring in Mathematics reports similar academic benefits for both, Primary and Secondary Education. Future research must be conducted as the superiority of Peer Tutoring in Primary over Secondary Education has yet to be proved in the Mathematics subject.