It's worth noting there are good reasons to believe the effects here are somewhat spurious – not "true" improvements but hollow gains akin to "teaching to the test." For instance, the top display of figure one suggests a fade-out effect with age, similar to the one seen with intelligence gains from pre-school programs (which disappear within a few years) [0]. Also, there's a reverse causality issue the authors don't fully control for, in the sense that more intelligent children are also more likely to persist longer in schooling.
As more and more careful studies were done on early childhood interventions, with larger sample sizes, the promising results of early investigations vanished. I expect the same will (largely) happen here.
When I learned about early education a long time ago, the argument was not about boosting short term cognitive abilities, as in this study about IQ tests, but long term socioeconomic improvement (i.e. we heard about changes in graduation, employment and crime).
As more and more careful studies were done on early childhood interventions, with larger sample sizes, the promising results of early investigations vanished. I expect the same will (largely) happen here.
[0] http://www.johnprotzko.com/wp-content/uploads/2015/11/Protzk...