It seems possible, as a minimum, that the supplementary private education that students have in Japan is one of the reasons that Japan does well in international assessments of standards. There was an article about these schools, the Juku, in a recent edition of the Economist. It seems that there is an expert on the subject of Juku. Here is his evidently knowledgeable blog posting on the Economist article. And here is the blog generally.
Here is an excerpt from his posting:
When Kenn refers to surveys in Japan that attribute juku attendance to shortcomings in education systems (an element of the article that has been picked up by some Twitter reactions to it already), I would offer a qualification – an important qualification, I think – that it is perceptions of shortcomings in Japanese education that seem to be driving parents and students to juku. Whether such shortcomings exist in an empirically demonstrable way is much less clear, and it is always interesting to note that it is not only perceived shortcomings in public education, but in private schools as well. Private school students in Japan also attend juku in large numbers after all.
I would suggest although it may not be possible with current means to demonstrate that the public education has shortcomings, it is worth considering the possibility that the parents have some understanding of what is going on!
It seems to me that so-called supplementary – nearly always private – education is quite a big story around the world. Huge amounts are written by educational experts, many of who are in mainstream public education and they normally write about public education. But there is another world out there and parents in many places are voting for it with their wallets.