Tell school to accept fool (6)
I believe the answer is:
snitch
'tell' is the definition.
(I've seen this in another clue)
'school to accept fool' is the wordplay.
'school' becomes 'sch' (abbreviation).
'to accept' indicates putting letters inside.
'fool' becomes 'nit' (both can mean a stupid person).
'sch' placed around 'nit' is 'SNITCH'.
(Other definitions for snitch that I've seen before include "Whistleblower (informal)" , "who tells on his classsmate?" , "Inform on someone in slangy way" , "I'm telling!" , "Inform on, tell tales" .)