This mixed methods study examined 73 5th graders' flow experience in a game-based science learning environment using two gameplay approaches (solo and collaborative gameplay). Both survey and focus group interview findings revealed that students had high flow experience; however, there were no flow experience differences that were contingent upon gameplay approaches. Results identified four game design features and student personal factors (reading proficiency) that significantly impacted student game flow experience. Students made significant science content learning gains as a result of gameplay, but game flow experience did not predict learning gains. The study demonstrated that the game was effective in supporting students' flow experience and science content learning. The findings indicated that the adapted game flow experience survey provided a satisfactory measure of students' game flow experience. The results also have implications for educational game design, as game design features that significantly contributed to students' flow experience were identified.