Young boys who did not own video games were promised a video-game system and child-appropriate games in exchange for participating in an "ongoing study of child development." After baseline assessment of boys' academic achievement and parent- and teacher-reported behavior, boys were randomly assigned to receive the video-game system immediately or to receive the video-game system after follow-up assessment, 4 months later. Boys who received the system immediately spent more time playing video games and less time engaged in after-school academic activities than comparison children. Boys who received the system immediately also had lower reading and writing scores and greater teacher-reported academic problems at follow-up than comparison children. Amount of video-game play mediated the relationship between video-game ownership and academic outcomes. Results provide experimental evidence that video games may displace after-school activities that have educational value and may interfere with the development of reading and writing skills in some children.