Persistent educational inequalities are a major concern in Dutch society. Despite decades of educational priority policy, the gaps in educational achievement between mainstream (native-born) children and children from low-income Dutch families and non-Western immigrant families remain substantial. This chapter reports evidence from a recent longitudinal study (the pre-COOL2–5 cohort study) on the effects of the current early childhood education and care (ECEC) policy for two to six year olds on early inequalities in language, cognitive and non-cognitive development. Although, the design of the pre-COOL study does not allow for strong conclusions, the results show that disadvantaged children who attend ECEC catch-up with their peers. The catching-up effect, moreover, is related to the quality of ECEC, and suggests added value of participating in high-quality ECEC for these children. Clear effects of ECEC quality on non-disadvantaged children’s development were not found, however. The sizes of the catching-up effects in disadvantaged groups are medium to strong, but the early inequalities are not fully reduced. Potential reasons are the relatively low intensity and late entrance in ECEC. Thus, both an earlier start and perhaps a more intensive programme are possible ways to enhance the effectiveness of preschool education priority policy.