Reduce inequality by increasing the number of school days

Some children have the bad luck to be born in a poor environment or a dysfunctional family. For them, school is the great equalizer that gives them a chance to still make in reasonably well in life. That works only if they can be in school and out of bad influence long enough (the "incarceration" hypothesis). Unfortunately, in areas where there are few school days and where especially the Summer break is long, all the good work is easily undone. In particular where there is inequality, we see the richer kids go to Summer camps to reinforce what they learned or learn some more, while the poor ones linger at home and forget a year's worth of school.

It is thus not surprising to see that Daiji Kawaguchi finds that fewer school days leads to more inequality. He looks at the 2002 school reform in Japan that abolished school on Saturdays. Comparing time diaries and test scores of students before and after the reform, he finds a dramatic change in the distribution. Students after the reform studied one third less at home, and the decline was even steeper in poor households. The impact on test scores is that the slope against socio-economic factors becomes 20-30% steeper. This is just from removing two half days of school a month. I wonder how this would translate in an international comparison where the school year ranges from 180 days in the US and France to 220 days in South Korea.