This report examines the effects on child poverty of expanding access to state-funded preschool for qualifying three- and four-year-olds. Subsidized child care is a key part of the social safety net that in effect boosts the resources available to low-income families by reducing a significant expense they might otherwise bear. At present, most subsidized child care and preschool programs in California require that families have incomes below specified levels--and often families must meet work requirements as well. The authors find: (1) Among the state's 1.03 million three- and four-year-olds, about 263,000 (26%) are currently served by public preschool programs; (2) Expanding access to preschool for low-income families in which all adults are working or in school--and only providing preschool for the hours needed for parents to work--could lower child poverty by up to 12 percent and could serve 263,000 more three- and four-year-olds. Using prevailing market rates, the authors estimate the potential state cost of this expansion to be $1.03 billion annually; (3) Expanding access to full-time care to all low-income children, regardless of parental employment, could lower child poverty by up to 24 percent and could serve 515,000 more three- and four-year-olds. At market rates, they estimate the potential price tag for this expansion to be $4.20 billion annually; (4) Latino and single-parent families would see the greatest poverty reductions from preschool expansions. For example, in the expansion to low-income working families, 44 percent of three- and four-year-olds moved out of poverty would be from single-parent families, although only 11 percent of young children live in single-parent families; and (5) State-funded preschool expansions that are open to families of all income levels would have the same impacts on poverty as the programs above. But research suggests universal programs can have additional educational benefits, especially for lower-income children. They estimate the potential costs of this kind of preschool program to be $1.32 billion annually if targeted to working families and $5.07 billion annually if provided to families regardless of parental employment. [This report was written with research support from Daniel Tan. For the accompanying Technical Appendices, see ED598078.]