An innovative system-building initiative known as the STEM Learning Ecosystems Community of Practice (SLECoP) is transforming U.S. STEM education through cross-sector partnerships between schools, afterschool and summer programs, libraries, museums, and businesses, among others. Although logic models exist to describe how SLEs can make positive contributions toward youth STEM learning in theory, it is unknown how individual SLEs are motivated or equipped to collect the evidence needed to demonstrate their value or abilities to solve the problems they were formed to address. The present study describes the results of a 34-item qualitative survey--completed by leaders of 37 SLEs from four U.S. regions--designed to understand where SLEs are in their evaluation planning, implementing, and capacity-building processes. We found that most SLEs were championed by the extended education sector, and all were highly motivated to conduct evaluation and assessment. Most communities reported a willingness to create a shared vision around data collection, which will help researchers and practitioners track, understand, and improve STEM quality and outcomes in and out of school.