Purpose: System reforms ask educators within and across organizational levels to interlace their individual practices into a collective practice so they can enact a different, more equitable schooling system for students. System reforms require educators to coordinate their work with their colleagues in ways they are not trained, incentivized, or supported to do, within systems that do not support collective practice. Yet educators' daily practices are the microprocesses that determine whether they accomplish the macro goal of coordinating a system and thus equitable opportunities for students. Research Methods: This embedded longitudinal case study examines changes in educators' mental maps around coordinating their daily practices as they implemented a new system reform, multi-tiered system of supports (MTSS). The observations, interviews, and artifacts document educators' implementation efforts in two elementary schools in the same district for 2 years. Findings: The findings illuminate how the implementation process can be inequitable, affording only some educators with opportunities to develop mental maps about collective practice. Professional learning opportunities that developed mental maps about collective practice possessed six design elements. These opportunities (1) focused on the system reform, (2) were embedded in daily practice, (3) required joint deliberations, (4) required system-wide membership, (5) were ongoing, and (6) occurred on-site. Implications: This article helps policy makers, leaders, and other reformers improve the learning opportunities they provide to educators responsible for coordinating children's learning opportunities. The article also highlights ways that implementation can be more equitable for educators.