Inform on school accommodating idiot (6)
I believe the answer is:
snitch
'inform on' is the definition.
(thesaurus)
'school accommodating idiot' is the wordplay.
'school' becomes 'sch'.
'accommodating' is an insertion indicator.
'idiot' becomes 'nit' (I've seen this before).
'sch' placed around 'nit' is 'SNITCH'.
(Other definitions for snitch that I've seen before include "Telltale (sl.)" , "who tells on his classsmate?" , "Inform on someone in slangy way" , "Grass" , "Inform on, tell tales" .)