A well defined line of research has been conducted on the role of self-efficacy (Bandura, A. (1977). Self-efficacy: toward a unifying theory of behavioral change. "Psychological Review", 84, 191-215.) in teaching and learning environments. The purpose of this study was to examine the effect of Laboratory-Based (LB) and Field-Based (FB) practicum experience on pre-service teachers' efficacy levels within one Physical Education Teacher Education program. The participants were 59 undergraduate students who were placed into two groups, LB design (n = 31) and FB design (n = 28). A quasi-experimental design with two levels of treatment and no control group was implemented. Both groups were administered a version of the Teacher Efficacy Scale (TES) adapted for physical education teachers at four stages of their preservice program: (1) at or near entry; (2) at the start of their methods course sequence; (3) at the end of the methods course sequence, just prior to student teaching; and (4) at program completion. Results from a Repeated Measures ANOVA indicated significant differences between groups on one facet of teacher efficacy at Stages 2 and 3. Those differences are attributed to the differing levels of authentic teaching practice between groups, and the challenges posed to each group of preservice teachers prior to student teaching. By the end of student teaching, both groups' efficacy levels were essentially equal, perhaps due to the similarly high level of authenticity across all subjects in that key experience. This study also highlights the importance of on-going, appropriate and authentic challenges in eventually establishing strong and stable efficacy levels among preservice teachers. (Contains 3 tables and 1 figure.)