Instructional routines, like "Number Talks" and "Notice and Wonder," engage students in doing and then talking about their mathematical thinking. Number Talk routines are short mathematical discussions where students mentally solve and share the strategies they used to make sense of the problem. In comparison, the Notice and Wonder routine asks students to reflect on a high-interest visual prompt with multiple entry points, share their noticings and wonderings, and then the teacher steers the discussion toward a mathematical question to explore further. But what happens when the Notice and Wonder routine is used in conjunction with a Number Talk? In this descriptive case study, we analyze whether and how this variation of a Number Talk provides a class of third-grade students opportunities to exercise agency. Findings from this study yielded two major themes: (1) agency is built when authority is shared during a mathematical discussion, and (2) Notice and Wonder is an instructional routine that supports sharing authority. We then discuss why this matters and next steps for research and practice.