In this districtwide scale-up, we randomly assigned seventh-grade students within 11 schools to receive a series of writing exercises designed to promote values affirmation. Impacts on cumulative seventh-grade grade point average (GPA) for the district's racial/ethnic minority students who may be subject to stereotype threat are consistent with but smaller than those from prior smaller scale studies. Also, we find some evidence of impact on minority students' standardized mathematics test scores. These effects address a substantial portion of the achievement gap unexplained by demographics and prior achievement--the portion of the gap potentially attributable to stereotype threat. Our results suggest that persistent achievement gaps, which may be explained by subtle social and psychological phenomena, can be mitigated by brief, yet theoretically precise, social-psychological interventions.