Recruitment is a key challenge for researchers conducting any large school-based study. Control is needed not only over the condition participants receive, but also over how the intervention is implemented, and may include restrictions in other areas of school and classroom functioning. We report here on our experiences in recruiting participants for random assignment experiments in public primary and secondary schools, often across midsize and large school districts. Our perspective is based on over twenty current and completed randomized controlled trials (RCT) in K-12 school settings conducted by SRI International, including studies of educational technology, literacy, mathematics, science, instructional materials, teacher professional development, and student behavioral supports, following What Works Clearinghouse standards for RCTs. A list of such studies appears in the Appendix, with an abstract for each study. Considering our experience across these studies, we reflect on how we approached the recruitment problem and what worked during our efforts. As we examined our own projects as case studies of how project leaders manage the problems, patterns of successful projects emerged.