For 25 years, the Gardner Center has worked in close partnership with school districts in the San Francisco Bay Area to develop research-informed policies, programs, and practices that support positive and equitable youth development. Several of these partnerships involve districts that are not part of a unified school district, meaning that students attend one district for grades TK-8 and another for grades 9-12. In the context of a multi-year project focused on building district capacity to support youth mental health and wellbeing, the Gardner Center observed a common thread of questions emerging from youth and adults that became even more salient post-COVID: As schools make efforts to support students' sense of belonging, what happens when students transition from their middle school district to their high school district? How do students experience belonging as they move through this transition? And, importantly, is there anything that districts can do (either individually or collaboratively) to support students' sense of belonging more systematically? The Gardner Center formed a working group with representatives from three districts to consider these questions. Through a series of conversations, the working group identified two common priorities. The first priority was to develop a better understanding of the research related to belonging and school transitions. To this end, they convened a broader group of representatives from all three districts as well as experts from multiple disciplines to discuss research, practice, and potential opportunities for collectively improving students' sense of belonging. The Gardner Center convened an expert panel to share key research about belonging and school transitions. The second priority was to better understand the experiences of students and parents as they move through the transition to high school. To support this goal, they conducted a pilot research project focused on exploring what "belonging" means to young people; how, when, and where they experience belonging in their day-to-day lived experiences; and what school structures, policies, and practices affect their sense of belonging as they transition to high school. The hope was that the findings from this pilot study could spark further collaboration, additional inquiry, and ultimately improvements in how the districts are fostering students' sense of belonging during this critical transition period. This brief highlights the lessons learned from this pilot study and identifies opportunities for supporting students' sense of belonging as they transition to high school.