In recent years, Dweck (2014) and Duckworth (2016) introduced two important concepts in student learning: mindsets and grit. These variables can drastically change the way individuals handle a learning situation, the degree of effort and persistence they display, and eventually, their level of achievement. Recent literature on self-theories recommends using domain-specific rather than domain-general instruments to explain school achievement. Furthermore, child samples are relatively understudied compared to adolescent and youth samples in terms of selftheories and achievement relations. This study focuses on math mindsets, academic grit, and their relation to math achievement at the primary school level. Math mindsets scale, academic grit scale, and a math achievement test were used as data collection instruments. Data were collected from purposively selected 225 4 th grade students in Istanbul, Turkey. A cross-sectional causal model has been tested through structural equation modeling (SEM). There was not a direct effect of growth math mindset but a significant negative effect of fixed math mindset on math achievement. The indirect effect of growth math mindset on math achievement mediated by academic grit was positive and significant; the indirect effect of fixed math mindset was nonsignificant. Finally, the effect of academic grit on math achievement was positive and significant. The SEM model explained 36% of the variance in math achievement and 64% of academic grit. School-based interventions are recommended to promote a growth math mindset and academic grit. Practical and theoretical implications are discussed in detail.