Abstract: This paper studies the use of knowledge in team decisions among new physicians as they acquire knowledge in residency training. I exploit a discontinuity in the relative experience of each trainee on teams to show that relative experience increases the influence of trainees in team decisions, as measured by the variance of their effects on spending. This increase in trainee effect variation across the discontinuity is larger for decisions requiring more discretion. Trainee effects usually 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.