LAUSR

Abstract Creating active classroom environments and reducing excessive student sitting requires changes in teachers' behaviours. This study examines a teacher training intervention, which aimed to increase the extent to which teachers use strategies to interrupt prolonged periods of students' sitting, as well as strategies to reduce total sitting time. The training was part of the Let's Move It (LMI) multi-level school-based intervention that aimed to reduce sedentary behaviour and increase physical activity among older adolescents, drawing on insights from social psychological theories, such as the reasoned action approach, self-regulation approaches and habit formation. We explore (1) whether the intervention increased teachers' use of sitting reduction strategies, (2) whether theoretical mechanisms mediated these changes, and (3) how teachers utilized habit formation. This pragmatic experimental study of vocational school teachers (n = 234) was embedded within a cluster-randomized controlled trial evaluating LMI, in which schools were randomized to intervention or no-treatment control arms. Three intervention workshops targeted skills and motivation to use sitting reduction strategies in class (e.g., active teaching methods, activity breaks). Participants self-reported sitting reduction activities, theoretical mediators, and use of behaviour change techniques (BCTs) at baseline and 8-weeks follow-up. Compared to controls, intervention schools' teachers increased breaks to interrupt sitting, but not their outcome expectations, perceived behavioural control or intentions – potentially due to ceiling effects. Effects were mediated by BCT use and perceived behavioural control. Descriptive norms mediated the effects of the intervention on intention, which in turn mediated the intervention effects on BCT use. BCT use and intention were positively related to reducing students' sitting.