We show that grit, a non-cognitive skill that has been shown to be highly predictive of achievement, is malleable in the childhood period and can be fostered in the classroom environment. Our evidence comes from an evaluation of a randomized educational intervention implemented in elementary schools in Istanbul. Outcomes are measured via a novel incentivized real effort task and actual school grades on core subjects. We find that treated students are 1) more likely to choose to undertake a more challenging and more rewarding task against an easier but less rewarding alternative, 2) less likely to give up after failure, 3) more likely to exert effort to accumulate task-specific ability, and consequently, 4) more likely to succeed and collect higher payoffs. The intervention also has a significant impact on school grades: We find that treated students are about 3 percentage points more likely to receive top grades in core academic subjects.