Prior research has demonstrated a male advantage in spatial skills and science achievement. The present research integrated these findings by testing the potential role of spatial skills in gender differences in the science performance of eighth-grade students (13-15 years old). In "Study 1" (N = 113), the findings showed that mental rotation ability mediated gender differences in physical science and technology/engineering test scores. In "Study 2" (N = 73,245), science performance was examined in a state population of eighth-grade students. As in "Study 1", the results revealed larger gender differences on items that showed higher correlations with mental rotation. These findings underscore the importance of considering spatial training interventions aimed at reducing gender differences in the science performance of school-aged children.