Manitoba students are struggling in mathematics. In the 2020/21 school year, 12.8% of Grade 9 students failed to earn their mathematics credit on their first attempt; this nearly triples to a 34.2% failure rate for Indigenous students (Manitoba Education and Early Childhood Learning, n.d.). Additionally, on the 2019 Pan-Canadian Assessment Program (PCAP), Grade 8 students in Manitoba had mean scores below the Canadian mean in all mathematics subdomains (O’Grady et al., 2021). Liljedahl (2016, 2021) found that students struggle to learn mathematics in traditional classrooms because teachers are planning lessons that do not require them to actively think. In response, he developed the Thinking Classrooms framework for teaching mathematics; it’s use has exploded in Kindergarten to Grade 12 classrooms in Manitoba, across Canada and around the world. While much research has been done to develop the framework and recommend effective practices for teachers, none has examined the role of school leaders who are expected to support it. This is problematic because policymakers are expending large amounts of money, time, and physical resources for teachers to create their own Thinking Classrooms while school leaders are left to muddle through. This study asks, what are the optimal practices for school leaders who want to support the mathematics instruction of teachers who are establishing Thinking Classrooms in K-12 schools? An interview-based qualitative research approach was used to learn from the experiences of teachers and school leaders in a large metropolitan school division located in Manitoba. The results are useful for school leaders who want to support their own teachers’ implementation of the Thinking Classrooms framework and improve the education of mathematics.