In this within-subjects design field experiment children's behaviour in the playground was charted as a function of gender and time in the classroom immediately preceding playtime. Playground behaviour was also related to post-recess classroom behaviour. Twenty-three 9-year-old children were observed for 14 weeks. Classroom behaviour (i.e., task relevant behaviour on standardised seat work immediately before and after playtime) and playground behaviour (i.e., social and non-social exercise and sedentary behaviour) were observed. Time in classroom before playtime was manipulated so that there was a shorter and a longer confinement period. Results indicated that children were less attentive to seat work as a function of time and that longer confinement resulted in more exercise for boys and more social sedentary behaviour for girls. Social behaviour at playtime and post-playtime attention to seat work were significantly related. Results are discussed in terms of Novelty Theory.