This study aims to understand the recurrent challenges of professional development school (PDS) partnerships experienced by many countries. It does so by conceptualizing PDS partnerships as endeavors to cross institutionally and epistemologically developed boundaries between teacher education, schooling, and academic research. After introducing what we call a "multilevel boundary crossing" approach, we look at the startup years of one academic PDS partnership, scrutinizing the successive learning mechanisms that were evoked at the institutional, interpersonal, and intrapersonal levels. The case study narrative illustrates the multilevel nature of boundary crossing and reveals different learning mechanisms in different phases and at different levels. For example, whereas coordination initially occurred at all levels, transformation occurred in later years mainly at the intrapersonal level. The study sheds specific light on the intrapersonal level by showing the significant and challenging role of various brokers in establishing both horizontal and vertical connections across and within the organizations involved. Despite being important leaders of the partnerships' activities, we observed how brokers prevented others from becoming more involved. We propose that partnerships should carefully consider the sort of learning processes they aspire to and can realistically expect at different levels and moments in time and accordingly consider how they want to position the various actors.