Reveal to a learner at school (3,2)
I believe the answer is:
let on
'reveal' is the definition.
(I know that reveal can be written as let on)
'learner at school' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'at' says to put letters next to each other.
'school' becomes 'eton' (famous UK public school).
'l'+'eton'='LET ON'
'to a' acts as a link.
(Other definitions for let on that I've seen before include "Pretend informally or permit to board" , "Reveal information" , "Divulge information" , "Divulge (secret to)" , "Disclose awareness" .)