Disclaimer.
I do not own Harry Potter.
Full stop.
Prologue: Hogwarts' Report Cards
Like any other school, Hogwarts kept a record of student's marks and kept them in a secret room that no-one except the house elves and staff knew the entrance to.
Which made them ever more elusive and coveted.
Sure, each student received their own marks, and friends knew each others', but enemies?
Nay, they could never compare.
But that is beside the point.
It just so happened that a new historian wished to recreate Hogwarts: A History, to the very last detail, and he just so happened to want the last fifty years of Hogwarts' report cards. Merlin knows why, but he did.
So McGonagall decided to look through the last fifty years of Hogwarts, to give the man what he wanted.
But it just so happened that McGonagall's window was open when she was reading the cards, and it just so happened that a strong breeze lifted all of them out of the window and blew them down into the lake.
And it just so happened that the Giant Squid could actually read.