School certificate achieved? Not entirely (5)
I believe the answer is:
teach
'school' is the definition.
(I've seen this before)
'certificate achieved? not entirely' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'TEACH' is hidden within 'certificate achieved'.
(Other definitions for teach that I've seen before include "Instruct, enlighten" , "Impart knowledge" , "Give instruction to" , "Tutor" , "Provide learning to" .)