interesting - I gather german education has lots of problems these days - across the board.
I wonder how that chart would have looked 30-50 years ago ? I get the feeling that there was a huge burst of mobility with the knock on effect of free senior and higher education? Maybe it wasn't across the board but lots of friends my age had parents who didn't go to uni / didn't stay at school long / studied higher ed at later age because families couldn't afford it but the kid ultimately stayed to 18 and went off to uni.
My Mum went to university in the 1950s after a free grammar education. The percentage of people who went to university then was very low. Her parents had left school at 14 I think and could no way have afforded to put a child through university these days. But I don't know how typical my mother's experience was - her parents were not "average" in many ways. Also, even if it was a typical experience, it can't be attributed to the existence of selection. It was because my mother was well taught up to A level (and this could happen now in a non-selective school) and the university experience was completely free of charge (fees plus maintenance grant) with nothing to pay back afterwards.
But back to "educational mobility" - this article seems to be measuring it according to the percentage of people who are better educated than their parents. It becomes problematic as more and more people become well educated - it's very hard for every generation to be successively better educated than its predecessor.