Am the only one who is baffled by their explanation of correlation? FTFA:

"correlation in educational attainment between a parent and a child is generally around .4 to .6. This basically means that, if my parent has one more year of schooling than your parent, I will automatically end up with 4/10 to 6/10 of an extra year of school than you have, all else equal."

This doesn't line up with my understanding of statistics