An assessment of the frequency with which low-income preschoolers (ages 3-6) experience unstable and multiple concurrent child care arrangements, and an examination of the effects of quality, stability, and multiplicity on children's social-emotional adjustment and school readiness. The study uses data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development, and aims to help policymakers understand how child care experiences affect the social-emotional adjustment and school readiness of children living in poverty.