This study examined the effects of training and feedback on instructor performance of Discrete Trial Teaching (DTT) and support skills. This included an examination of the generalization and maintenance of instructor skills, and the impact of instructor skills on student performance. Six undergraduate research assistants received an 8-hour training in DTT and taught a variety of skills and behaviors to four preschool students who had developmental disabilities. A multiple-baseline design was used to assess instructor performance following training alone, during implementation of oral and written performance feedback, and at 2, 4, 6, and 10 weeks follow-up. Instructors demonstrated correct use of DTT and related skills at a rate of 63-80% following training. When performance feedback was provided, all instructors attained proficiency ratings of 90% by the second session and 97-100% by the fourth session. High levels of instructor proficiency were maintained at follow-up and generalized across students and learning tasks. Student learning and instructional efficiency were superior in the feedback and follow-up conditions compared to baseline. The results highlight the need for training programs that allow school personnel to correctly use DTT to effectively facilitate learning and development in students who have developmental disabilities. (Contains 2 tables and 1 figure.)