Research using an experimental design is needed to provide firm causal evidence on the impacts of child care subsidy use on child development, and on underlying causal mechanisms since subsidies can affect child development only indirectly via changes they cause in children's early experiences. However, before costly experimental research is undertaken, it is important to identify potential causal mechanisms to include in such research. The purpose of this study is to test potential causal mechanisms to explain the negative relationship between child care subsidy use and cognitive development found in previous research. This study tests the direct relationship between child care subsidy use during preschool and child developmental outcomes at kindergarten entry, and it also tests two plausible causal mechanisms that may explain the relationship between child care subsidy use during preschool and children's cognitive development at kindergarten entry. (Contains 2 footnotes and 1 exhibit.)