There is a growing knowledge base in mathematics education highlighting the importance of teachers' cognizance about what and how they are noticing, namely considerations about their attending, interpreting, and decisions to respond on the basis of students' thinking. However, less focus has centered on those in teacher leader positions and how those individuals may arrive at claims about students' thinking and use evidence to support their assertions, meaning how they notice. As a result, a process to engage teacher leaders in considering students' thinking was implemented for professional growth for those who support mathematics teachers. Findings highlight the degree of specificity of the teacher leaders' noticing, the origin of the evidence they cite, and their connection between claims about students' mathematical thinking, evidence, and broader implications for teaching and learning. Most teacher leaders included limited or robust evidence, with a majority citing transcript quotes as evidence for their claims about student thinking. Most teacher leaders were noticing at a mixed (Level 2) or focused (Level 3) level, based on a four-point scale. Implications for those working with mathematics teachers or teacher leaders to support the development of noticing and how to cite evidence are provided.