As states and districts expand access to publicly funded PreK programs, researchers and policymakers have been grappling with experimental evidence demonstrating that the benefits of PreK on academic skills are not likely to last into early elementary school. A leading hypothesis to explain this phenomenon is that PreK and the elementary grades are not aligned with respect to content and mode of instruction. The Boston Public Schools Department of Early Childhood has begun to implement an aligned curriculum and professional development model called Focus on Early Learning to address this issue. The current study describes the components of this aligned model, identifies the facilitators and barriers to implementation, and examines the extent to which the model has been implemented to date. Findings demonstrate that a critical component of Focus on Early Learning is a combination of aligned structures and rich instructional content. A number of structural and process factors have facilitated implementation, but the district has also faced barriers, including funding and the challenge of creating a culture that supports alignment. Although survey and observational data suggest that PreK and kindergarten teachers are implementing the curriculum at moderate levels, there was significant variation in implementation across the study sample. In addition, teachers were less likely to receive professional development to support implementation. Although teachers generally supported the idea of aligning instruction across grades, they were less likely to engage in specific activities to do so, such as having common planning meetings with teachers across grades. Implications are discussed. (author abstract)