This field-experimental study evaluates an intervention in which students complete a self-directed “self affirmation” exercise that encourages them to identify and reflect upon their core personal values. This within-classroom randomized trial was conducted among 2,500 7th and 8th graders from six Philadelphia-area middle schools during the 2008–09 and 2009–10 academic years. Although this study failed to replicate earlier findings indicating that the affirmation generated large increases in the academic performance of minority students, this treatment did lead to statistically significant improvements in the performance of the minority students in more supportive classroom environments. However, the treatment contrast also reduced the performance of female students in those settings.