Analyzing data from students in the NCES High School Longitudinal Study dataset, we drew upon expectancy-value theory to examine the role of student motivation (measured by self-efficacy, identity, utility, and interest), as mediators between 9th grade math test scores and final math GPA for autistic students. In predicting final high school math GPA, math identity was the strongest predictor for autistic students with above average test scores. Findings for autistic students contrast with results for non-autistic students whose final math GPA is strongly predicted by the direct effects of 9th grade test scores. These results suggest that seeing oneself as a “math person” may be particularly influential for autistic students with higher 9th grade math performance.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10803-022-05522-1.