Fool among classmates (3)
I believe the answer is:
ass
'fool' is the definition.
(both can mean a stupid person)
'among classmates' is the wordplay.
'among' says the answer is hidden in the clue.
'ASS' can be found hidden inside 'classmates'.
(Other definitions for ass that I've seen before include "Horse relative" , "An American backside" , "Stupid person or American bum" , "Titania loved one" , "Silly fool or beast of burden" .)