One of the primary skills required by mathematics teachers is the ability to provide effective explanations to their students. Using Kay's (2014) theory-based framework for creating instructional videos, this study explored the quality and growth of explanations embedded in mathematical instructional videos created by 37 pre-service teachers (female = 26, male = 11). The Instructional Video Evaluation Scale (IVES), comprised of four constructs (establishing context, explanation heuristics, minimizing cognitive load, engagement), was used to assess the quality of two videos (pre-feedback and post-feedback). The initial video created by pre-service teachers (pre-feedback) revealed a number of problem areas, including providing a clear problem label, using visual supports, noting potential errors that might occur, writing legibly, highlighting key areas, listing key terms and formulas, being concise, and using a clear, conversational voice. After receiving detailed feedback based on the IVES, the ratings of the second video (post-feedback) for each of the initial problem areas increased significantly. The IVES scale, grounded on Kay's (2014) framework, helped identify and improve the effectiveness of pre-service teachers' explanations of mathematics concepts.