This study is a longitudinal examination of the impact of therapist stage of training on client outcomes in psychotherapy. The study included 22 PhD-level psychologists who work in a university counseling center (8 female, 14 male) who had completed at least 2 training periods in the center where data were gathered. Therapists worked with 4,047 clients, and 40,271 sessions were included in our analyses. Clients were given the Outcome Questionnaire-45 (OQ-45) on a session-by-session basis, tracking treatment response. The effect of stage of training on both the magnitude and speed of OQ-45 change was examined through hierarchical linear modeling. Therapists were found to achieve the same amount of change or less change on average in their later stages of training. Therapists were also found, on average, to achieve the same rate of change or a slower rate of change in later stages of training. Findings suggest that as therapists progress through formal stages of training, they do not improve in their ability to effect change in their clients. Given these findings, a better understanding of expertise in psychotherapy practice and how to develop it may be an important area for future theory development, research, and training program development. We call for further work examining if and how an individual therapist can become more effective with time.