Supervisors who have the opportunity to work with more advanced trainees are those most likely to encounter Level 3 therapists. We consistently note throughout this book that levels of therapist development are not synonymous with a particular number of practica, years of experience, or age. Trainees (old and young, highly experienced and inexperienced) move at their own speed through the developmental levels. One can, however, encourage this growth by pro viding appropriate supervision. Recall that Wiley and Ray (1986) found that supervised experience influences trainee growth, while unsupervised therapy experience is unrelated. A stimulating environment and corrective feedback are necessary for therapists to continue to develop and improve at their trade, a result that is consistent with the research literature on learning (Anderson, 2005).