The USAID/Kenya Primary Math and Reading (PRIMR) initiative is a task order under the USAID Education Data for Decision Making (EdData II) project that operates in collaboration with the Kenyan Ministry of Education, Science and Technology (MoEST) and USAID/Kenya, and implemented by RTI International. The program is a randomized controlled trial intervention that included formal (public or government) schools and low-cost private schools (LCPS) located in Nairobi, Kiambu, Nakuru and Kisumu counties. PRIMR and its Kenyan partners created, published, and distributed new teaching and learning materials, based on the existing Kenyan curriculum; designed and led professional development to build the skills of educators and improve student literacy outcomes; and introduced a number of innovative teaching methods. Teachers and head teachers received training to encourage active learning and participation by both girls and boys in the classroom and were further supported with frequent visits and advising by trained instructional coaches. By mutual agreement among the MoEST, USAID, and RTI, approximately 500 formal schools and LCPSs located in Nairobi, Kiambu, Nakuru, and Kisumu counties were to participate in the PRIMR Initiative. To choose the sample of formal schools, the project team first selected all eligible zones from within the selected locations, then randomly assigned a subset of zones to groups that would receive the PRIMR treatment in phases (Cohorts 1, 2, and 3). Across all three cohorts, 262 formal schools were selected. Sampling for LCPSs began by clustering the schools into geographic groups of either 10 or 15 schools from across Nairobi’s divisions. Twenty clusters then were randomly assigned to Cohorts 1, 2, or 3, stratified by geographic region. The number of LCPSs selected was 240. In January 2012, the Cohort 1 schools (125 schools: 66 public, 59 LCPS) began implementing the reading interventions using PRIMR-designed materials and techniques, and the math intervention followed beginning in July 2012. The Cohort 2 schools (185: 65 public, 120 LCPS) began reading and math interventions in January 2013. Cohort 3 schools (101: 51 public, 50 LCPS) served as a control group for most of the program, and then began receiving the full intervention during the final stages of PRIMR (January 2014). In addition, it was decided that the 2014 phase of the intervention would be extended to all 547 remaining schools, rather than only to Cohort 3 as originally planned. As a result, the number of pupils benefitting increased from 12,755 in January 2012 to 56,036 in January 2014. Randomly selected students from all treatment and control schools were assessed via administration of a combined Early Grade Reading Assessment (EGRA), Early Grade Mathematics Assessment (EGMA), and Snapshot of School Management Effectiveness (SSME) at three time points: baseline, midterm, and endline. The PRIMR Initiative’s research design included several “experiments within an experiment.” These consisted of a study of three different combinations of information and communication technology (ICT) as teaching and learning aids in selected schools in Kisumu County; a longitudinal study of about 600 students who were assessed at all three time points, with their reading and numeracy competency levels compared and contrasted across the assessments; and MoEST-driven policy research on various education issues at the national level.