The optimum situation for a school system is one in which bureaucratic influences and practices support classroom learning. The study reported in this policy brief examines a transformation toward this state of affairs in the country's eighth largest school district, the 140,000-student San Diego City Schools. An unusual leadership arrangement allowed the district to build and nurture new instructional supports based on research, create significant changes both in the central office and at school sites, and forcefully direct a process that replaced traditions with effective learning practices. San Diego went into policy territory usually avoided by large urban districts. It used the tools of the bureaucracy to craft a district-wide professional learning culture based on research, performance data, and feedback on teaching practice. Its "boom" strategy, the antithesis of the usual incremental efforts to gain buy-in, was followed immediately by specific support structures, giving the leaders a chance to root all parts of the system in common design principles about instruction. Lessons for other large districts are discussed briefly. [This Brief is based on the following CTP Research Report: "San Diego's Big Boom: District Bureaucracy Supports Culture of Learning," January 2002 (Amy Hightower).]