Similarly, language development starts at the middle level, increases to the high level at around ages 1-2, slightly decreases towards age 4, and will continue to decrease towards the middle and low levels from then on. Numeracy starts with the low level, increases rapidly from ages 1-3, gradually decreases but will be maintained at the high level from age 4 (Figure 5.1 and OECD, 2015b). Children who are already falling behind in the first few years of their childhood face greater obstacles to catch up and succeed at school and beyond (Naudeau et al., Participation in early childhood education is crucial.