Informed about student dialect (5)
I believe the answer is:
slang
'dialect' is the definition.
(thesaurus)
'informed about student' is the wordplay.
'informed' becomes 'sang' (I've seen this in other clues).
'about' means one lot of letters goes inside another.
'student' becomes 'L' (as in L-plates for learner drivers).
'sang' going around 'l' is 'SLANG'.
(Other definitions for slang that I've seen before include "Patois" , "Unconventional language" , "type of language?" , "Berate" , "Argot" .)