District schools and charter schools are often at odds. When the two school types share a school building--arrangements known as "co-locations"--the tensions can boil over. But what happens when district and charter leaders approach co-location as a tool to promote school improvement, rather than simply a real estate deal? Based on fieldwork in four improvement-focused co-locations, this report shows that sharing space across sectors doesn't have to result in a pitched battle, but that leveraging co-location for school improvement is not easy. Even with strong district and charter leadership, teachers can struggle to understand the goals of improvement-focused co-locations. Cross-pollination around school culture can be a productive starting point for collaboration, but collaboration on instruction is much harder to achieve. With considerable effort and resources, district and charter schools can peacefully coexist, but using co-location for school improvement is a daunting task whose full costs and benefits are, to date, still uncertain.