Several active-learning pedagogies involve groups of students working together to construct their own understanding of course content. In these classrooms, the instructor serves as a facilitator of learning, by interacting with every group, engaging students in discussions, answering questions, and providing formative feedback. This type of interaction can be challenging for instructors in large enrollment classes. The use of undergraduate teaching assistants (TAs) during active-learning "lecture" periods is an effective way to provide an active-learning experience to a large group of students. Most undergraduate students have little to no experience with facilitating active-learning environments. Therefore, it is important to provide a thorough TA training experience in order for TAs to be effective in an active-learning classroom. Using an iterative design process, several successful strategies were developed to help prepare undergraduate TAs to assist in facilitating a large organic chemistry active-learning class. These methods ensured that TAs were knowledgeable about the content, could address questions effectively, and could provide formative feedback to students. TAs reported that these training methods were instrumental in improving their classroom facilitation and understanding of chemistry content.