It is. My point was that “compulsory schooling versus a bit more compulsory schooling” is what they are measuring and not “less educated vs more educated”. I t

It is. My point was that “compulsory schooling versus a bit more compulsory schooling” is what they are measuring and not “less educated vs more educated”. I too would expect a difference in outcomes between more and less compulsory schooling. But I would expect it from the non-education related impacts of it (I.e. de-facto childcare and keeping the kids/teens from engaging in as much long-term harmful activities)