Research by psychologists and economists demonstrates that many non-cognitive skills are malleable in both children and adolescents, but we have limited knowledge on what schools can do to foster these skills. In a field experiment requiring real effort, we investigate how schools can increase students’ perseverance in math by shaping students’ beliefs in their abilities to learn, a concept referred to by psychologists as “mindset.” Using protocols adapted from psychology, we experimentally manipulate students’ beliefs in their ability to learn. Three weeks after our treatment, we find persistent treatment effects on students’ perseverance and academic performance in math. When investigating subsamples, we find that students, who prior to the experiment had less of a belief in their ability to learn, generate the treatment effect. The findings suggest that a low-cost intervention focused on students’ mindset can improve students’ engagement and performance.