Leadership development is a topic of widespread interest; however, relatively little is known about the developmental process or factors that might influence it. To address this shortcoming, the personal change trajectories of participants (N = 1315) engaged in team-based action learning projects (k = 205) to promote leader development were estimated using multilevel growth modeling techniques. Evidence was found in support of differences in the initial leadership effectiveness levels across participants as well as differences in the shape or form of their personal trajectories. Based on recent theorizing on leader development (Day, Harrison, & Halpin, 2009), hypotheses were proposed and tested predicting that adopting a leader identity would serve as a within-person, time-varying covariate of leadership effectiveness and that goal orientation would serve as a between-person, cross-level moderator of the personal change trajectories. Results suggested full support for the role of leader identity and partial support for goal orientation, with the most consistent and beneficial effects associated with a high mastery or learning goal orientation.