Previous research suggests that early childhood education and care (ECEC) participation is positively associated with educational outcomes of especially disadvantaged children in both targeted and universal ECEC systems. ECEC has also been found to reduce early learning disparities between children with immigrant and non-immigrant backgrounds, which is linked to its potential to support early language acquisition. Consequently, ECEC has been regarded as a way for promoting equality of opportunity and has become an integral part of family policy in Western societies. As ECEC has become embedded in family policy, it is important to move beyond mere participation rates and examine how different features of ECEC, such as starting age and intensity, are linked to educational outcomes for children from diverse backgrounds. Interestingly, in contrast to international findings, Finnish research has not found evidence that ECEC can compensate for the educational outcomes of disadvantaged children. Comparing results across countries is challenging due to significant differences in their ECEC systems. For instance, although the Nordic countries are often grouped under the same Nordic welfare model, the institutions that guide families’ childcare choices vary between these countries. Finland stands out from the other Nordic countries particularly in its childcare policy following parental leave. Compared to its Nordic peers, Finland provides relatively extensive support for home care of young children through the home care allowance (HCA) cash benefit, which has resulted in considerably lower ECEC participation rates. Therefore, the relationship between ECEC and children's outcomes should be examined both within and across countries. In this dissertation, I examine the relationship between ECEC and children's educational outcomes in Finland and the Nordic countries. As the theoretical framework of the study, I draw on the mechanisms of accumulation, compensation, and multiplication, which enable an examination of how ECEC is connected to children’s educational outcomes among children from different backgrounds. Dissertation is built upon three sub-studies. The first study examines how the age at which children begin ECEC is associated with their literacy test scores at age 15 in the Nordic countries. The study utilizes PISA data from the years 2015 and 2018 and applies multilevel linear regression analysis. Based on the results, it is possible to compare literacy scores among children who started ECEC at different ages, across various family backgrounds, and in different countries. The second study investigates how the duration of the HCA period is associated with children's literacy grades at age 16. The study utilizes comprehensive Finnish population register data and applies sibling fixed-effect regression analysis. The results allow for an examination of how the length of the HCA period relates to children's literacy skills across groups defined by parental education level and ethnic origin. The third study examines how the intensity of ECEC is associated with the speech production of 4-year-old children. The study utilizes data from the 2018 Child Health, Wellbeing and Services survey, collected during child health clinic visits. Logistic regression analyses are used to examine the association between children's average weekly hours in ECEC and their speech production, with results presented separately by parental education level. This enables an investigation into whether ECEC intensity is linked to children's educational outcomes across different family backgrounds. In line with previous international research, this thesis finds that universal ECEC has the potential to compensate for educational outcomes among children from low SES and immigrant backgrounds (Articles II and III). Thus, ECEC may promote equality of opportunity even in countries with universal ECEC systems. These findings support the European Commission’s goals to further increase ECEC participation across Europe. Therefore, while expanding access to ECEC can promote gender equality by enhancing mothers’ labor market participation, it also holds promise for reducing disparities in educational outcomes among children from diverse backgrounds. However, the findings from Article I did not indicate a compensatory effect; rather, the associations appeared additive or, in Norway, even more beneficial for children from high-SES families. Thus, further research is needed.