Come up again in core curriculum (5)
I believe the answer is:
recur
'come up again' is the definition.
(I've seen this in another clue)
'in core curriculum' is the wordplay.
'in' says the answer is hidden in the clue.
'RECUR' is hidden within 'core curriculum'.
(Other definitions for recur that I've seen before include "come back to one's mind" , "Perseverate" , "Happen again (5)" , "Repeat" , "expected to return" .)