... their partner joins a posh school - discount to follow (5)
I believe the answer is:
ensue
'follow' is the definition.
(I've seen this before)
'their partner joins a posh' is the wordplay.
'their' becomes 'ens' (I can't explain this - if you can you should give a lot more credence to this answer).
'partner' becomes 'e'.
'joins' means one lot of letters go next to another.
'a posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'e' after 'u' is 'ue'.
'ens'+'ue'='ENSUE'
'school discount to' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ensue that I've seen before include "Happen as consequence or afterward" , "Result in a particular way" , "Follow as a consequence" , "Befall" , "Happen afterwards as a result" .)