Innovators are exploring new designs for the primary and secondary education system under the umbrella of personalized learning, but consensus is lacking on a precise definition of personalized learning or on which component practices are essential. Practitioners and policymakers seeking to implement personalized learning are creating custom designs for their specific contexts. Those who want to use rigorous research evidence to guide their designs will find many gaps and will be left with important unanswered questions about which practices or combinations of practices are effective. Despite the lack of evidence, there is considerable enthusiasm about personalized learning among practitioners and policymakers, and implementation is spreading. Thus, the purpose of this Perspective is to offer strategic guidance for designers of personalized learning programs to consider while the evidence base is catching up. This guidance draws on theory, basic principles from learning science, and the limited research that does exist on personalized learning and its component parts. [This project is a RAND Venture.]