May I ask you Dr Moriarty, did your parents apply for you to go before you were 14 and you were accepted on academic ability?
Yes, I'd been enrolled in the "feeder" primary school seven years earlier so had a kind of right of way, I suppose. The pressure for places probably wasn't as great then, and we lived nearby, too.
Also, the fact that I was young for my class was something of an accident — where we lived abroad, the school year ran from January to December, so I kind of skipped a half a year on the way out, and again on the way back, and ended up in the year ahead of my classmates from seven years previously. They looked at my records from the schools attended abroad and gave me a (fairly perfunctory) ability test and on that basis decided there was no point in putting me "back" a year.
That was all a long time ago. Perhaps more relevant is the experience of friends of ours living in Indonesia who decided to send their eldest girl (16) to board in an expensive private girls' school in South Dublin (with a view to third-level prospects, I guess, since they don't see themselves returning to live in Ireland anytime soon). The poor kid was utterly miserable and, despite being great at sports and having no real difficulty on the academic side, refused to return and is now back in an international school in Indonesia.
Point being that there's a lot more to the choice of school than simply academic reputation/
Sunday Times "league table" results. The secondary school I attended in Dublin was/is considered one of the "better" ones, and I can assure you that I came across some dreadfully incompetent teachers there (mostly old priests). I didn't play rugby, absolutely hated the place, and whatever success I had at the Leaving Cert and subsequently had very little to do with the quality of the education I got there.
I suggest you look at other schools for your son, specifically on the socialisation of a teenage boy settling in a new place. If you want him to transfer to the IoE for the Leaving Certificate, that's a decision for later.
This, in a nutshell. If you find he's set his heart on a high-points degree course and are worried that he won't get the necessary results, then by all means transfer him in sixth year (or simply get him some good grinds). In the meantime I'd be more concerned to find a school where he feels comfortable, fits in, and enjoys what are meant to be the "best years of his life".