For students to thrive in the U.S. educational system, they must successfully cope with omnipresent demands of exams. Nearly all students experience testing situations as stressful, and signs of stress (e.g., racing heart) are typically perceived negatively. This research tested the efficacy of a psychosituational intervention targeting cognitive appraisals of stress to improve classroom exam performance. Ninety-three students (across five semesters) enrolled in a community college developmental mathematics course were randomly assigned to stress reappraisal or placebo control conditions. Reappraisal instructions educated students about the adaptive benefits of stress arousal, whereas placebo materials instructed students to ignore stress. Reappraisal students reported less math evaluation anxiety and exhibited improved math exam performance relative to controls. Mediation analysis indicated reappraisal improved performance by increasing students' perceptions of their ability to cope with the stressful testing situation (resource appraisals). Implications for theory development and policy are discussed. [At time of submission to ERIC this article was in press with "Social Psychological and Personality Science."]