This post is one in a series highlighting MDRC's methodological work. In the past decade, rapid growth in the number of charter schools and school district choice systems has provided education researchers with exciting opportunities to use naturally occurring pockets of randomization to rigorously study the effects of policy-relevant education reforms that are already in place, often on a large scale. When a lottery is used to decide which students receive the opportunity to attend a school, it can create the conditions for a natural experiment. Because students' school assignment is random, researchers can identify the causal effect of the school model on students. This paper discusses naturally occurring school lotteries, which most often take place within relatively simple school-managed processes or within centrally managed admissions processes, and how MDRC researchers utilized both admission processes in studies.