Move from ESF to Intl School - retaking a year!

Am interested in people's opinions on the following situation.
My son is currently in K1 at an ESF kindergarten. His birthday is in November 2008 so he falls into the year group catchment of kids (ie. all 2008 birthdays) who all started K1 this year (2011), and is one of the youngest in his year.
I am however keen to get him into an International school (ideally Kellett, HKA or HKIS) whose year group catchment is Aug-Aug. In accordance with these entry requirements, my son will fall into the year group of kids who commence K1 NEXT year (2012).
If I apply to these Intl schools and we are successful in getting a place at one, he will most likely have to retake K1.
My concern is whether him redoing a year at this young age will have any detrimental effect on him?! Do you think he will even know!? Do you think this is the right option or (if we are lucky enough to get a place) should I request that he enter K2 at the Intl school? Do you think it doesnt really matter (other than the fact that we have paid for a year's schooling at an ESF kindy when we might not have needed to?!) My main concern is that he will find things easy as he will be redoing stuff he has already learnt and may just 'coast' along and become lazy rather than being challenged.

Just in case of interest, I have put him into the ESF system now just in case we are unsuccessful in gaining a place at the International School of our choice.

Thanks for anyone's thoughts or similar experiences.
KK

First a bit of a clarification.

For HKIS (and I assume other schools) you son would need to be 4 by September 1 of the year he starts. On September 1, 2012, your son will be 3.75 years old so the entry date of 2012 you wrote should be 2013, shouldn't it?

Hong Kong International School

"Reception One – students must be aged 4 years by September 1, of their year of entrance."

School at such young age is about exploration and excitement. International school learn through play and experience anyways, there isn't much that he will feel. Ores or even be too much ahead by "repeating" a year. He would be excited in making new friends, meeting new teachers etc. as Lon as he is in a different classroom with different teachers, that would be fine. I know 2 December born children when has stayed behind at my Son's kindergarten because the parents do not feel that they are quite ready for yr 1 yet.

The school is nice enough to put them in a different classroom (they only have 2 K2 classes). And the boys are doing fine. So no worries!

Not sure if relevent, maybe, but I never started school till I was 6, so didn't get any schooling before my 6th birthday, and there was no detrimental effect (many years on a mathematics degree, qualified in a profession and all that). I've got kids that age now and as lottie says, its about play, exploration and socialisation at that age and I personnally believe there is little value in anything academic they learn at that age. Your son will be just fine.