Multisite, course-based undergraduate research experiences (CUREs) in the Ecological Research as Education Network (EREN) were assessed for impacts on student learning of collaborative science skills using a survey that could serve as a starting point for a validated assessment instrument for multisite CUREs. Pretests/posttests were administered across multiple courses and institutions, capturing effects of diverse EREN projects and pedagogies on collaborative knowledge. Students' scientific collaboration and data management skills improved most in small, upper-level courses. The amount of EREN content in a course was positively associated with posttest scores for 60 to 86 percent of assessment survey questions. However, no learning gains were seen for some questions, and some cases of low competency and effects of timing and place of assessment testing were observed in student scores. EREN CUREs need further development to maximize their potential.