Although students with stronger executive functions (EFs) tend to do better on math computation (MC) assessments than students with weaker EFs, stressful testing situations may lower or affect their mathematical ability. Rumination is one maladaptive coping strategy that can negatively affect EF processes, but little is known about how it impacts the relationship between EFs and MC. This study aimed to examine the relationship between students' performance on a standardized MC task and ratings of EF ability as a function of their level of rumination. In a sample of students from Grades 4 to 6 (n = 72, mean age = 10.74), there was an interaction between EF scores and rumination in predicting MC. Students with weaker EF scores demonstrated worse math performance than students with stronger EF scores. Interestingly, their level of rumination moderated this association. Specifically, EF difficulties were only associated with less proficient MC performance among high ruminators; this association was not observed among those students reporting low rumination levels. For school psychologists, these findings provide insight into the potential causes of poor MC performance among students with average or better EFs.