BackgroundIn times of accelerating changes, teachers who proactively engage in activities towards school improvement and innovation are increasingly needed. Still, studies on factors that affect teachers' proactive behaviour are rare.AimsIntegrating previous research on proactive behaviour within the Job Demand–Resources (JD‐R) Model, this paper investigates how job characteristics (time pressure, bureaucratic structures, participative climate, personal initiative of the team) and aspects of teachers' professional competence (self‐efficacy, self‐regulation skills and knowledge) contribute to and interact with their proactive behaviour.SampleA total of 130 German secondary school teachers (M(SD)age = 44.05 (11.36), 65% female) participated in this study.MethodsWe employed a full two‐wave panel design, with measurement points 5 months apart. The data were analysed with (moderated) single indicator modelling and a cross‐lagged panel model.ResultsWhile teachers' self‐efficacy in implementing change and self‐regulation skills predicted their concurrent proactive behaviour, job characteristics and teachers' knowledge had no such cross‐sectional effects. In addition, we found an interaction effect of time pressure and teachers' self‐efficacy on proactive behaviour. Including the second measurement point, data indicated no cross‐lagged effects of the job and personal factors on proactive behaviour. However, cross‐lagged analysis revealed that teachers' proactive behaviour predicted their later self‐efficacy in implementing change and the time pressure they perceive.ConclusionsExamining both cross‐sectional and longitudinal effects, this study highlights the importance of measurements over time when analysing factors that influence teachers' proactive behaviour: While aspects of professional competence appear to be trainable concurrent resources, time pressure can limit their effect. Finally, cross‐lagged effects of teachers' proactive behaviour on their later self‐efficacy and time pressure appear as influential in the long run.