@SeaofTranquility - I can relate to your DS dilemma as DC was there a few years ago. Also had been pooled but rejected and went on to get all A stars. They did reapply and were successful - really thrived at Cambridge, didn’t find the work too taxing; had a full on social life and involvement in loads of societies and came out with a first and in top 3 of cohort. I say this only to prove the randomness of the Cambridge selection process - so much depends on the interview on the day.
In terms of reapplying, the way I (personally!) would look at it is this -
It’s probably only worth the risk of reapplying if they have perfect grades. This is because in STEM over half of students actually in the uni will have achieved all A stars and in humanities over a third. So applying with all A stars in hand you are positioning yourself in the top half (STEM) or top third (humanities) of those actually there (hope that makes sense).
Between his last application and next Oct, has he done anything ‘extra’ to make his application stand out - eg, essay competitions , school prizes - anything like that?
A tutor said to me that if a student is going to reapply (and many do successfully), basically don’t give them a reason to turn you down! If they have perfect grades AND something like an essay competition win / commendation, subject prize or something else ‘standout’, they probably have a good chance with a fair wind at interview. They will expect a bit more of post A-level applicants - they will be comparing them to the students they’re actually teaching. Also, they will want to hear a clear plan for the gap year.
I hope this helps to think things through. I don’t know what subject he’s applying for though (sorry, should have asked as essay comps etc may not be relevant if it’s STEM).