Investment in the early years was largely driven by scientific evidence from programs such as Head Start, the Abecedarian Project, and the Perry Preschool Program. These three programs showed how attending daycare and preschool can have a significant impact on children's cognitive and non-cognitive development.
These programs generally shared some key characteristics. First, they were randomized trials. Access for families and children was determined by lottery, functioning like a raffle, in order to prevent factors such as individual characteristics, parental involvement, or the student's background from determining children's participation in these programs. This made it possible to isolate the impact of daycare or preschool attendance, preventing other factors from contaminating the analysis.
Furthermore, both the Abecedarian and Perry Preschool Programs were implemented on a small scale, raising questions about their sustainability and the possibility of replicating them in larger contexts. There is therefore a debate about their long-term impact and what steps we need to take to identify the characteristics that guarantee the robustness of their results.
Head Start—the best-known and most widely implemented program—shows results that vary depending on the metrics used and the timing of the evaluation. Some analyses point to positive short-term impacts (upon leaving preschool), which then seem to fade around age 11 or in middle school. However, in the long term, positive effects are observed in areas such as the likelihood of accessing higher education or behavioral aspects, including the risk of depression or the incidence of illegal behavior in adulthood.
Two other cases deserve attention. The first is a preschool program in Boston that covered children between the ages of three and five. Once again, in a randomized experiment, some children moved from part-time to full-time coverage. Thanks to centralized official records, it was possible to follow these children over time. Positive impacts were observed, especially at the end of secondary school, namely a higher probability of completing compulsory schooling, better results in higher education entrance exams, and higher university enrollment rates.
A program in Tennessee—also large-scale and covering about three-quarters of the state's children each year—shows opposite results. Between 2009 and 2010, children's access was also determined by random lottery in regions with excess demand. Initially, children who attended preschool performed better in literacy and numeracy at the end of the program. However, when reassessed in 6th grade, these effects had completely disappeared.
Two patterns emerge from all these examples. On the one hand, there is no consensus on the long-term impacts on school performance. On the other hand, the positive effects are often more pronounced in children from more disadvantaged socioeconomic backgrounds and in non-cognitive and behavioral dimensions.
Further research is therefore needed to enable us to answer not only the question of access to preschool, but above all the type of access, namely:
This is also a key point in the current debate on preschool and daycare: scalability. Scaling up these programs often means that the investment per child is lower, coupled with a reduced capacity for continuous monitoring of their implementation. It is precisely in this process that the much-desired lasting effects can be lost. In the Portuguese context, marked by the necessary expansion of the daycare network in view of the still limited supply, this is therefore a particularly relevant issue in the near future.