In 2008 the San Francisco Unified School District (SFUSD) confronted a problem that has been growing for decades. It boasted the highest academic performance of any large urban district in California, yet its achievement gap was widening, as too many African American, Latino, and low-income students fell far behind their classmates. The achievement gap was the greatest challenge facing the school district--one that revealed systemic disconnects throughout its schools and programs, beginning with its youngest students. This report tells the story of how the district began narrowing the gap by rethinking its approach to teaching and learning in pre-K, kindergarten, and the early grades of elementary school. District leaders worked to align curricula, professional development, assessments, and even classroom layouts across the PreK-3rd grade continuum, initially focusing on connections between pre-K and kindergarten. To lead this ambitious effort, the district turned to its underfunded and sometimes overlooked Child Development Program, which ran its pre-K classrooms. SFUSD has been building a bridge between pre-K and third grade, beginning by strengthening its public pre-K program. Doing so generated support among successive superintendents and district leaders, and allowed early learning leaders to expand the strategy to a growing network of schools. This progress was fueled by San Francisco's long-standing commitment to early learning and a core of committed partners. In addition, it has been supported by a growing national recognition that a PreK-3rd grade approach is among today's most effective education reforms. Within the district, changes unfolded in a series of overlapping phases: (1) gaining traction among a wider circle of district leaders; (2) bridging the typically separate worlds of pre-K and elementary school; (3) implementing strategies to more schools across the district; and (4) revamping professional development. The district's successes and struggles developing its PreK-3rd approach hold lessons for other school districts exploring the approach in California and around the nation: (1) Begin with a strong platform; (2) Work with local partners; (3) Hire leaders with the right skill set; and (4) Take a system-wide approach. Contains notes.