Abstract: What causes professionals in organizations to practice differently in similar situations? This paper studies practice variation in team decisions, among physicians in residency training who frequently switch teams and are randomly assigned patients. I identify the effect of relative experience on a trainee's influence in team decisions by a discontinuity in relative experience across the one-year tenure mark. The influence of senior trainees is larger for decisions requiring more discretion. Trainee effects generally fail to converge through training but show serial correlation consistent with learning and are not explained by trainee characteristics or training histories. These findings suggest variation due to idiosyncratic learning and tacit knowledge.