Mature reason that stops one revealing programme (6)
I believe the answer is:
agenda
'one revealing programme' is the definition.
'agenda' can be an answer for 'programme' (agenda is a kind of programme). I'm not certain of the 'one revealing' bit.
'mature reason that stops' is the wordplay.
'mature' becomes 'aga' (I can't explain this - if you can you should believe this answer much more).
'reason' becomes 'end' (I've seen this in other clues).
'that stops' indicates putting letters inside (to stop can mean to block a gap).
'aga' going around 'end' is 'AGENDA'.
Can you help me to learn more?
(Other definitions for agenda that I've seen before include "Plan for meeting" , "Programme of business" , "Something perhaps hidden" , "Table of business" , "List of items to be dealt with" .)