In contrast to the well documented male advantage in psychometric mental rotation tests, gender differences in chronometric experimental designs are still under dispute. Therefore, a systematic investigation of gender differences in mental rotation performance in primary-school children is presented in this paper. A chronometric mental rotation task was used to test 449 second and fourth graders. The children were tested in three separate groups each with different stimulus material (animal drawings, letters, or cube figures). The results show that chronometric mental rotation tasks with cube figures--even rotated in picture plane only--were too difficult for children in both age groups. Further analyses with animal drawings and letters as stimuli revealed an overall gender difference in response time (RT) favoring males, an increasing RT with increasing angular disparity for all children, and faster RTs for fourth graders compared to second graders. This is the first study which has shown consistent gender differences in chronometric mental rotation with primary school aged children regarding reaction time and accuracy while considering appropriate stimuli. (Contains 3 figures.)