Mindfulness enhances emotion regulation and cognitive performance. A mindful approach may be especially beneficial in high-stakes academic testing environments, in which anxious thoughts disrupt cognitive control. The current studies examined whether mindfulness improves the emotional response to anxiety-producing testing situations, freeing working memory resources, and improving performance. In Study 1, we examined performance in a high-pressure laboratory setting. Mindfulness indirectly benefited math performance by reducing the experience of state anxiety. This benefit occurred selectively for problems that required greater working memory resources. Study 2 extended these findings to a calculus course taken by undergraduate engineering majors. Mindfulness indirectly benefited students’ performance on high-stakes quizzes and exams by reducing their cognitive test anxiety. Mindfulness did not impact performance on lower-stakes homework assignments. These findings reveal an important mechanism by which mindfulness benefits academic performance, and suggest that mindfulness may help attenuate the negative effects of test anxiety.