This study aimed to examine the effects of a physical education teacher education programme on (a) preservice teachers' (PSTs') specialised content knowledge (SCK), and (b) the game-play development of their students, during a student-centred Sport Education-Step Game Approach (SE-SGA) unit. Three PSTs selected by convenience sampling (22-24 years old), their 60 eighth-grade students (three classes: 38 boys, 22 girls, M[subscript age] = 13.3), and a mentoring team (one teacher educator, one university supervisor, and one cooperating teacher) participated in the study. The PSTs participated in a two-stage programme where they learned how to teach volleyball using SE-SGA, and then implemented an SE-SGA unit during their school placement. Using audio/video data from 30 lessons, we examined PSTs' SCK (content development, depth of content knowledge) on a lesson-by-lesson basis. We also assessed the 2v2 game-play performance of PSTs' students across three assessment points. Descriptive statistics were computed for SCK scores and repeated measures analysis of variances were used to analyse variance in game-play variables over time. Results showed improvement in PSTs' SCK and students' game-play. The PSTs showed strong SCK, with index levels above the 3.0 cut point, and progressive use of informing, refining, and applying-game tasks over time. Students improved in most game-play variables (namely 'serve', 'reception', 'setting') and the 'game performance index' over time. Student game-play development seemed to be strongly influenced by an interdependent interaction between PSTs' SCK and additional situated, model-based features of content development (i.e. extensive application of knowledge in competition events, the problem-solving focus of the refining tasks).