This research explores the implementation of growth mindset with high school mathematics students. I conducted a secondary analysis of case study data gathered for the Ontario Association for Mathematics Education (OAME) Grade 9 Applied Collaborative Inquiry Project. I questioned how these mathematics educators understood mindset, the strategies they used to foster growth mindsets, and their perceptions of the value of, and obstacles associated with, using a mindset approach particularly within a streamed mathematics course context. The observations describe these teachers’ efforts to embed mindset into their mathematics classrooms as well as their sense of how ingrained fixed mindsets, views of mathematics as a right or wrong subject, marks-based assessment practices, and the streamed nature of the Applied mathematics course, may discourage growth mindset. These observations highlight the importance of ensuring that approaches to fostering growth mindset permeate every aspect of classroom practice, effectively calling for change in many secondary mathematics norms.