Grade school topic (7)
I believe the answer is:
grammar
'grade school topic' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for grammar that I've seen before include "Functions and relations of words in sentences" , "Correct usage of words" , "A language's syntax and morphology" , "type of school" , "Study of word and sentences" .)