This report describes evaluation design in PFS projects, with a focus on early childhood education (ECE). It is part of a larger toolkit for states, localities, and investors considering early childhood PFS projects and is based in part on stakeholders' experiences with ongoing PFS projects. In the first part of this report, we outline the role of evaluation in a PFS project and the importance of considering evaluation design early. The second part of the paper provides a high-level overview of three categories of evaluation design, including randomized controlled trials (RCTs), which are generally considered the most rigorous evaluation design. In the final section, we review considerations for planning an evaluation in the context of ECE programs. (author abstract)