Early years are a critical period for skill development. In this sense, the Early Childhood Education and Care (ECEC) programmes have an important role in promoting children's learning during this period. This study aimed to explore the effectiveness of ECEC programmes by analysing the relationship between students' ECEC attendance and their later academic proficiency using PISA 2015 data. PISA results show that across the OECD countries, students who had attended ECEC tend to have higher scores in academic proficiencies at the age of 15. However, these differences in academic proficiencies between those who attended ECEC versus those who did not attend are almost nil when students' socio-economic status (SES) is considered. This relationship reflects differential access to learning opportunities for children from deprived contexts. Furthermore, results show that entering ECEC programmes earlier than the typical time is associated with lower proficiencies at the age of 15. Therefore, earlier entry to ECEC is not necessarily beneficial. Learning benefits of ECEC provision vary considerably across PISA countries illustrating the importance of a country-specific policy context and the quality of their ECEC provision. The analyses of several quality indicators point out that the improved quality of ECEC programmes is associated with higher academic skills at later stages. These results highlight that mere attendance to ECEC programmes is not enough to ensure better academic performance. The quality of the educational provision, especially concerning those students from disadvantaged backgrounds, should be ensured.