What happens when you introduce preschool education across an entire country? In Japan, between 1964 and 1970, the government pumped money into expanding kindergartens. And researchers Michihito Ando and colleagues saw their chance: what does such a reform do to young people in the long run?

Using a clever design—looking at regions that benefited from the reform to varying degrees—the researchers found something remarkable. Ten to twenty years later, the number of arrests for youth violence fell, and teen pregnancy was reported less often. And this was in a country where the rates were already low. What didn’t change: how many young people went to high school or college.

Here is an important distinction: the study tries to go beyond pure correlation, but really tries to make a causal assessment. They used differences between provinces in the speed of expansion, tested for pre-trends and performed placebo tests. They did this as follows: they examined whether adults who did not receive pre-school education during the reform period (born before the reform) also showed changes in crime or pregnancy during the same period. If that were the case, then the effect might be due to something other than pre-school education, such as a general trend or policy that affected everyone.

But guess what? They find no effect in those older groups. There was no change in adult crime or pregnancy rates around the reform period. That increases the credibility of their conclusion: that the decline in young people is really due to preschool education, and not to broader societal changes. They were thus able to essentially rule out alternative explanations, such as other policy measures or economic shocks.

But then the big question: what explains the effect? ​​More years at school? No, they saw no change there. More mothers at work? Nope. The most likely explanation, according to the researchers, is better non-cognitive skills. Japanese preschool education does not focus on numbers or letters, but on social-emotional development. This is in line with previous studies that show programs influencing behaviour, such as impulse control or dealing with others, reduce the chance of risky behaviour later in life.

Important detail: the mothers of the children in the study had relatively low levels of education. This makes the findings particularly relevant for countries where this is also the case. A universal system can therefore work, even if it is not aimed at a specific disadvantaged group. 

Abstract of the study :

The evidence for the effects of early childhood education on risky behavior in adolescence is limited. This paper studies the consequences of an expansion of a universal preschool program in Japan. Exploiting regional differences in the program expansion, we estimate the policy effects using an event study model. Our estimates indicate that the preschool expansion significantly reduced juvenile violent arrests and the rate of teenage pregnancy, but did not increase high school enrollment or college enrollment rates. We suspect that improved non-cognitive skills can account for the reduction of risky behavior in adolescence.