Checking son's in further education (11)

I believe the answer is:

restraining

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'checking son's' is the definition.
'restraining' can be an answer for 'checking' ('restrain' can be a synonym of 'check'). I am not sure about the 'son's' bit.

'further education' is the wordplay.
'further' becomes 'res' (I can't explain this - if you can you should give a lot more credence to this answer).
'education' becomes 'training' (synonyms).
'res'+'training'='RESTRAINING'

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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