Background: According to the Self-Determination Theory, satisfaction of basic psychological needs for relatedness, competence and autonomy is a necessary basis of motivational self-regulation in students. Supportive academic contexts are expected to satisfy these basic needs. Aims: We aimed to explore the mediating effect of motivational self-regulation strategies in the relationships between the provisions of emotional support, guidance and reassurance of worth from peers and academic achievement in adolescents. Sample and Methods: A total of 463 students enrolled in compulsory secondary education were recruited for the study. The students completed self-report measures of perceived social support and motivational self-regulation strategies, and their academic grades were noted. The data obtained were examined by regression mediational analysis. Results: Overall, peer support had a significant effect on self-regulated motivation. Several motivational regulation strategies had a mediating effect on the relationship between perceived support from peers and academic achievement. Conclusions: Considering the nature of the mediational strategies, peers seem to encourage autonomous types of regulation and address the lack of motivation in students. Thus, in the light of our findings, peer support must be considered in creating a classroom climate that is conducive to engagement and learning.