The Big Lift is a collective impact initiative extending from preschool to third-grade in San Mateo County, California. The initiative is a partnership of the Silicon Valley Community Foundation, the San Mateo County Office of Education, and the County of San Mateo. Launched in 2012, the initiative aims to boost children's reading proficiency in San Mateo County through four different types of activities, called "pillars": (1) High-Quality Preschool; (2) Summer Learning; (3) School Attendance; and (4) Family Engagement. RAND is conducting a multiphase evaluation of the initiative, including an implementation study of the pillars and descriptive analysis focused on the outcomes of children who received Big Lift programs. This report provides the first set of descriptive analyses of participation in two of Big Lift's pillars -- preschool and summer learning -- and measures of readiness at kindergarten entry for the children enrolled in the four Cohort 1 districts: South San Francisco Unified, Jefferson Elementary, La Honda Pescadero Unified, and Cabrillo Unified (the first round of funded school district communities). [This report was commissioned by The Big Lift along with the Silicon Valley Community Foundation with funding from the County of San Mateo. For this report's technical appendix, see ED595039. For the related research brief, "The Big Lift Preschool, Two Years In: What Have We Learned so Far?," see ED594887.]