Persistence is an important part of student success--both in and out of school. To enhance persistence, we first need to assess it accurately. Digital games can be used as vehicles for measuring and enhancing persistence. The purpose of this study is to test the effects of (a) game-level characteristics (i.e., game mechanics and conceptual difficulty), and (b) student-related characteristics (e.g., students' incoming knowledge and gender) on persistence in a game called "Physics Playground." The participants in this study were 137, eighth and ninth-grade students from a K-12 school in Florida. We used a Hierarchical Linear Modeling Approach (HLM) to analyze the data. The major findings are (1) the degree of difficulty relating to both the physics concepts and game mechanics of each game problem are significant predictors of persistence, with the former being more effective than the latter in predicting students' persistence, and (2) the number of gold and silver trophies students attained in the game were the only significant student-level predictors of persistence. We conclude by discussing the findings, the implications, limitations, and future research related to this study. [For the corresponding grantee submission, see ED612081.]