As soon as you hear the children shrieking at the playground on School, well...
The shriek on The Wall, was lifted from "Careful With That Axe Eugene", shrieking has been Waters' forte since the early days of PF.
OTOH, Syd, David and Roger met at a private school they all hated, so the kids shrieking sorta could be counted as inevitable discovery, if it were an invention. And the syncopated guitar was a late, resisted addition added by Bob Ezrin only to part 2.