This mixed methods study examined the flow experience of 5th graders in the CRYSTAL ISLAND game-based science learning environment. Participants were 73 5th graders from a suburban public school in the southeastern US. Quantitative data about students' science content learning and attitudes towards science was collected via pre-and post surveys. Quantitative and qualitative data about students' game flow experience was collected using an adapted game flow scale and focus group interviews. The findings demonstrated that students had high flow experience in the game; however, there were no flow experience differences that were contingent upon gameplay conditions. The results revealed important factors that impacted students' flow experience, including key game design features and student individual differences such as reading proficiency and peer interaction during gameplay. Students made significant content learning gains, but their attitude towards science did not change as a result of gameplay. Flow experience was not found to be a predictor of science learning gains. The results make contributions to the understanding of the effectiveness of game-based learning and the application of flow theory with elementary school students in a game context. Results also have implications for educational game design. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]