Mental rotation is a spatial cognitive ability malleable by training, e.g., physical education. The importance of children’s physical activity on their self-concept is also well proven. The present study examines whether a ten-week boxing training improves ten-year-old children’s mental rotation performance and self-concept. Forty-five children (26 boys and 19 girls, age: M = 9.62, SD = 0.71) completed a mental rotation test and filled out a questionnaire about their academic, physical, and social self-concept. Seventeen of the children participated in a ten-week boxing training. After the training, all children completed the same test and questionnaire. Results showed that children in the training group improved more than children in the control group in all three aspects of self-concept and mental rotation performance. All interaction effects between time and group were moderate to large. We conclude that a ten-week boxing training successfully improves children’s self-concept and spatial abilities.