People with disabilities are chronically underrepresented in many geoscience departments across the country. There are a number of proposed reasons why this under-representation persists, one of which is lack of instructor training in designing accessible curriculum and making high-quality accommodations. This not only puts students with accessibility needs at a disadvantage academically but also creates an unwelcoming environment. We determined through a broad survey of the instructors and undergraduate students that the geology department at a large research-focused university lacked sufficient instructor training on accessibility-related topics. We designed and implemented a scenario-based training at the university department scale to begin correcting the lack of training. Our training was designed for and given to teaching assistants (TAs), and we assessed the effectiveness of our training by measuring TA knowledge gain and retention throughout the fall 2017 semester; comparing the number of students approaching TAs with accessibility needs in the training year to years prior to the training; and gauging undergraduate feelings of inclusion throughout semester via a series of minute-paper style surveys. Our results show an increased baseline understanding of universal design and semester-long retention of that knowledge. The number of students approaching TAs with accessibility needs increased compared to years prior to the training, and undergraduates reported overall feeling that their TAs had a genuine interest in their learning as individuals. We conclude that our results merit the inclusion of an accessibility focused TA training in the annual training schedule.