Sport education (SE) has been touted as a model particularly conducive to realizing affective objectives. The purpose of the current study was to investigate the influence of a training programme on one preservice physical education (PE) teacher’s ability to promote moral and sporting behaviour in SE. The participants in the study were the teacher, Alex, and the 75 middle school students he taught within two 20-lesson SE Ultimate Frisbee seasons. The theories of structural development and social learning guided data collection and analysis. Data were collected with nine qualitative methods and reduced to themes by employing analytic induction and constant comparison. Many of the students in the study had been socialized into norms of sporting participation that were mostly negative and believed that it was acceptable to behave in an unfair and unsporting manner. During the course of the two seasons, Alex managed to get many of them to question this thinking and to engage in positive sporting behaviours. That he did not change the thinking or behaviours of some highly skilled students, and that the behaviours of other students of similar skill level regressed once the seasons became more competitive, illustrated how powerful the negative influences of the institution of organized youth and school sport can be.