The learning situations created by the Tactical Games Model (TGM) hold great promise in influencing student motivation. Situational interest is a type of motivation related to person-activity interactions (Chen, Darst, & Pangrazzi, 1999). The TGM sequence (Game 1–Q & A–Situated Practice–Game 2) offers a variety of purposeful learning situations that invite the person – activity interaction required by situational interest. The purpose of this study was to examine student motivation during an eight-day water polo unit by using the theoretical frame of situational interest. Participants were one middle school physical education teacher and twenty-two 5th and 6th grade students. Teacher data were collected using one-hour interviews (initial, midpoint, and exit), informal conversations (before, during, and after class), and a modified TGM Teacher Performance Checklist (Fisette, Bohler, Carpenter, & Griffin, 2006). Student data were gathered using a modified Interest Survey (Mitchell, 1993) at the start and end of unit, TGM learning situation (Game 1, Q & A, Situated Practice, and Game 2) questionnaires each lesson, and focus group interviews at the end of the unit. Data were analyzed using open and axial coding, concept mapping (Rossman & Rallis), content analysis, and theoretical comparisons (Strauss & Corbin, 1998). Results show that students did not experience automatic instances of situational interest based on the type of learning situation (i.e. Game 2). An instance of situational interest occurred when a student or students experienced a positive student – learning situation interaction that lead to a level of enjoyment. Meaningfulness and/or success variables were necessary for students to experience a positive student – learning situation interaction. Students who found a learning situation meaningful communicated that the learning situation helped them improve their skills and game play. Students who experienced a positive interaction due to success talked about being able to apply skills or movements they were practicing, play the game, and/or win the game. Negative interactions related to lack of meaningfulness were student reports about not seeing the reason for the learning situation or not finding the learning situation helpful in their development of skills or improvement of game play. Student profiles confirmed that each individual TGM learning situation had the potential for either a positive or a negative student - learning situation interaction. Personal interest in physical education, personal interest in water polo, the appeal of a learning situation, and skill level in water polo were not strong predictors of situational interest. Keyword(s): active participation, middle school issues, physical education PK-12