Concerning American exam which they took again (5)

I believe the answer is:

resat

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'took again' is the definition.
(exam)

'concerning american exam' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'american exam' becomes 'sat' (standard attainment test, UK exam. I am not sure about the 'american' bit.).
're'+'sat'='RESAT'

'which they' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for resat that I've seen before include "did test again" , "Took (exam) again" , "Took another chance to pass" , "was tested again" , "went back to the paper" .)

I've seen this clue in The Irish Times.

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