We used self-report surveys to gather information on a broad set of non-cognitive skills from 1,368 8th-grade students attending Boston public schools and linked this information to administrative data on their demographics and test scores. At the student level, scales measuring conscientiousness, self-control, grit, and growth mindset are positively correlated with attendance, behavior, and test-score gains between 4th- and 8th-grade. Our results therefore highlight the importance of improved measurement of non-cognitive skills in order to capitalize on their promise as a tool to inform education practice and policy.