Reveal information, having left school (3,2)
I believe the answer is:
let on
'reveal information' is the definition.
(I've seen this before)
'left school' is the wordplay.
'left' becomes 'l' (common abbreviation).
'school' becomes 'eton' (famous UK public school).
'l'+'eton'='LET ON'
'having' acts as a link.
(Other definitions for let on that I've seen before include "Divulge information" , "Pretend, feign" , "Tell me" , "Be revealing" , "Pretend informally or permit to board" .)