The benefits of peer mentoring in school settings are well-documented, however, the focus has been on the perceptions of teachers, as opposed to teaching assistants, who report distinct beliefs about their professional development. A mixed methodology was used in which 304 primary school teaching assistants completed questionnaires regarding their views of their professional development while undertaking training on a mathematics intervention for underachieving pupils. Open-ended questions elicited the perceived benefits of the peer mentoring aspect of the training. We utilized Lave and Wenger's (1991) community of practice framework to inform the qualitative analysis and the principles of grounded theory to arrive at three themes representing the perceived benefits: an opportunity to discuss and share experiences; increased confidence; and a safe space to test teaching plans and resources. Findings were used to reframe the benefits of peer mentoring for teaching assistants undertaking intervention training, which can inform further research and future training programs.