Because I have memorised terabytes of the sodding stuff.
How far in hundredths of a mile is every school within a five mile radius? Which is the only local school whose 5 A*-Cs (incl E&M) has increased despite the English shenanigans? What is a Language Aptitude Test, how does it differ from Verbal Reasoning and how many places at school X are awarded based on it? Which ability band had the widest catchment at Dunraven last year and should I advise DD accordingly when she takes the test? How do the Kingsdale music scholarships work? (that last one was rhetorical, nobody actually knows that).
I wouldn't mind so much, but it's looking increasingly likely that DD will go to a girls' school so we'll have to do it all again in two years time for DS.