Aspiring teachers must develop an in-depth understanding of high-quality instructional practices. In order to prepare, instruct, and coach aspiring teachers, the National Institute for Excellence in Teaching (NIET) has developed a the NIET Aspiring Teacher Rubric (ATR) based on principles of excellence in instruction. This research brief summarizes measurement properties of the NIET ATR to assess aspiring teacher instruction during a classroom observation conducted by a trained and certified observer. Results of the analyses provide strong evidence that the NIET ATR is a valid and reliable tool to measure aspiring teacher instruction. Moreover, the NIET ATR is capable of distinguishing variation in aspiring teachers' performance, allowing for more specific and meaningful feedback for aspiring teachers.