Playing video games is a pervasive activity among middle school students. Researchers are now investigating whether such play carries any educational benefits. One aspect of many video games is teamwork. The goal of the present research was to investigate whether playing video games cooperatively with or competitively against others affects later teamwork behavior and team performance. 60 middle school students, all without previous video game playing experience, participated in the present study. They were randomly assigned to one of three experimental conditions: no video game playing, cooperative video game playing, and competitive video game playing. Those in the video game conditions then were taught how to play Modern Warfare 3 and played for two hours. They were randomly paired with another subject from the same condition and either played with or against that person. Two weeks later, all participants were randomly paired with new partners from the same experimental condition and played a Prisoner’s Dilemma game where points are awarded to players based on whether they play cooperatively or competitively with each other. Total team scores were tallied after 20 trials. Results showed that those who played Modern Warfare 3 cooperatively scored the highest, while those who played it competitively scored the lowest. Results suggest that video game playing can bolster teamwork and team performance when played cooperatively and impair teamwork and team performance when played competitively.