Grit, the inclination to pursue long-term goals with passion and perseverance, predicts academic achievement and professional success, but how to encourage grit in students remains an open question. The goal of the current study was to understand how perceptions of school culture influence the development of grit in middle school students. We conducted a year-long, prospective, longitudinal study (N= 1,277) examining grit, perceived goal structures (mastery vs. performance), and academic achievement. In cross-sectional analyses, we found that students who perceived their schools as more mastery goal-oriented were grittier and earned higher report card grades. In contrast, students who perceived their schools as more performance goal-oriented were less gritty and earned lower report card grades. In longitudinal analyses, changes in perceived mastery school goal structure predicted changes in grit over the school year, which in turn predicted changes in grades. Changes in perceived performance school goal structure, in contrast, did not reliably predict changes in grit. These findings suggest that school environments that emphasize the value of learning for learning's sake may encourage children to sustain interest in and effort toward long-term goals.