Abstract:  The main purpose of this study was to compare the performance of grade-skipped students with their peers in mathematical reasoning and applying. In this study, gender and mathematical self-concept were considered as effective variables. This study was a part of a longitudinal study.  The data analysis was performed through repeated measurements and the results showed that in applying math concepts, grade-skipped students outperformed their peers. However, there was no significant difference between grade-skipped students and their peers regarding the reasoning; although the 4^th-grade students are better than the 3th-grade. The girls and boys showed the same function on applying, reasoning and between grade-skipped students and non- grade-skipped. Mathematical self-concept was also similar in three groups. It seems that grade-skipping does not have negative effects on math performance. Of course considering other academic contexts, emotional and social aspects and pursuing the effects of acceleration in long-term is necessary for informed decision-making in the field of grade-skipping.