This study investigates the relationships between preschool quality and children's learning and development from fall to spring of 1 school year through the analysis of child- and program-level data from approximately 70,000 children, ranging in age from 4.5 to 5.5 years old, in 1,700 Quality Counts California (QCC) rated preschool programs, the majority of which were center-based California State Preschool Programs. Learning and development was assessed using children's fall and spring scores on three domains of the Desired Results Developmental Profile, a developmental assessment administered by children's classroom teachers. The authors used multiple regression models to estimate the additional months of learning and development associated with attending a higher-rated program (Tier 4 or Tier 5) above and beyond the months of learning and development projected for a child attending a program rated Tier 3. The relatively small number of programs rated Tiers 1 and 2 were excluded from the analysis. The study suggests that attending a higher-quality-rated program is associated with greater learning and development than attending a lower-quality-rated program. [This report was co-produced by the Berkeley Evaluation and Assessment Research (BEAR) Center at the University of California, Berkeley, with additional support from the California Department of Social Services.]