Deliberate practice and having a growth mindset have been hypothesized to increase school performance. But previous studies are few, have been limited to very short interventions, and on average resulted in small effect sizes on school performance. This study compared the attitudes, performance, and behavior of 130 7th-grade students taking part in eight 30-minute sessions of deliberate practice and growth mindset over 14 weeks to a same-age active control group. The intervention had no significant effects on attitudes related to deliberate practice, growth mindset, or mathematical performance. However, students who participated in the intervention engaged in more deliberate practice behavior in a mathematics test. We pre-registered our hypothesis and research design at aspredicted.org/13742.