Ghosts
Every primary school in the land is actually haunted, usually by dead children who were killed when an unstable playground wall fell on them, although sometimes it's a dreadful fire which engulfed the building in Victorian times.

Bizarrely, a simple wall fall will often result in several gruesome ghosties, whereas the school itself burning down will always leave just one rather dull (and mute) dead girl wearing a dirty white dress who Jenny swears was watching her in the toilets at break.
written by Os*ar*Ter*y, approved by Conor