This study addressed the need for empirical tests of the global instructional design (ID) model as a toolkit for classroom teachers in authentic settings; and the performance improvement challenge of finding effective, efficient methods of professional development for preparing graduate assistants to teach. Participants were eighteen teaching assistants (TAs) with primary instructional responsibilities at a large Midwestern university. Twelve were given a training intervention in instructional design, while the other six served as a control group. The intervention was based on the iterative, five-phase ADDIE model, and principles from educational psychology. Dependent measures were TAs' ID knowledge, teaching self-efficacy, satisfaction with knowledge and strategies, perceived teaching competence, teaching performance and teaching effectiveness, and their students' engagement and perceived learning. All of the study's seven hypothesized relationships were found statistically significant. The intervention, though brief, measurably increased the ID knowledge of participating TAs, along with their teaching-related self-perceptions, and student outcomes. Instructional design emerges as a potentially powerful training tool for organizing teachers' and trainers' knowledge related to the complex practice of classroom instruction. (Contains 1 figure and 2 tables.)