Guided by Self-Determination Theory (SDT; Ryan & Deci, 2000; Ryan, Williams, Patrick, & Deci, 2009) and Achievement Goals Theory (Elliot & McGregor, 2001), this study examined how coach supports affected intrinsic motivation (IM) and how mastery-approach (MAp) goals mediated the relationship between coach supports and IM among a group of underserved adolescents. Participants were 93 boys (M[subscript age] = 11.91 years, SD = 1.22) at a summer sports camp in the southwestern U.S. Seventeen questions from previously validated questionnaires measured participants' IM, MAp, and perceived coach supports. Three mediation models were examined to test the mediating effects of mastery-approach goals. The results of the three mediation models revealed that perceived coach supports positively predicted IM (ßs > 0.38, "ps" < 0.05). MAp goals had a large medication effect on the relationship between perceived coach supports and IM (ßs > 0.29, "ps" > 0.05, ?[superscript 2]s > 0.25). The data from the study suggest that coaches provide supports for children in autonomy, competence, and relatedness based on SDT. At the same time, we recommend focusing on MAp goals in order for coach supports to generate positive influences on children's IM.