External accountability pressures force school leaders to examine how they support effective teacher practice. Providing collaborative work time to evaluate student performance and plan for future teaching has been a common strategy to support teacher practice. We assess how teachers from two districts with differently-structured curricular policies talked about mathematics lesson planning. This analysis reveals three concrete steps that school leaders can take to support teachers in ways that encourage more substantive collaborative planning: provide guidance related to curricular materials and sequencing of topics; define expectations governing content of meetings; and specify how teachers should prepare for formal meetings.