Comprehensive school event is after examination (9)
I believe the answer is:
extensive
'comprehensive' is the definition.
(similar in meaning)
'school event is after examination' is the wordplay.
'school' indicates an anagram (school can mean to improve or manipulate).
'after' is a charade indicator (letters next to each other).
'examination' becomes 'ex' (I am not sure about this - if you are sure you should believe this answer much more).
'event'+'is'='eventis'
'eventis' anagrammed gives 'tensive'.
'tensive' after 'ex' is 'EXTENSIVE'.
Can you help me to learn more?
(Other definitions for extensive that I've seen before include "Comprehensive" , "Exist even being wide-ranging" , "terribly large" , "Covering a large area" , "Broad in scope" .)