Reveal learner joining college (3,2)
I believe the answer is:
let on
'reveal' is the definition.
(I know that reveal can be written as let on)
'learner joining college' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'joining' says to put letters next to each other.
'college' becomes 'eton' (Eton College, English private school).
'l'+'eton'='LET ON'
(Other definitions for let on that I've seen before include "Divulge information" , "Be revealing" , "Reveal information" , "Tell me" , "Pretend, feign" .)