Thank you so much everyone for taking the time to reply. I'm sorry it's taken me so long to come back to this thread - we've been busy with spring break and then getting back in to school.
Hilda - thank you, I'll check out those threads.
Desert - sadly it was too early for wine, and is too early now too! I'm sorry to hear that your boys had a tough start in their first school, and glad to hear that they are much happier in their new school. Ours were definitely ready for the break - they missed the half term that they would have had in the UK, and then spring break was only a week. They have 11 weeks off over the summer which seems insane to me, I'd much rather it was spread out a bit!
Crazycat - Again, sorry to hear that you had such a bad start, that must have been so difficult. We are nowhere near needing to go home, thank goodness, although in some ways that makes it hard in a different way as I don't think we are at the "nothing to lose" point either. The local school is not awful, and the kids are doing OK most of the time. And we can't be sure that they would be happier in the private school.... it's very difficult!
Chips - It's interesting that you feel it took your son a whole year to settle. Thing is, whenever we talked to anyone about moving, and our concerns about the kids, without exception everyone says breezily, "Oh, the kids will be fine, they are so flexible, yadda yadda". But it isn't that simple! Yes they are "fine", in that I don't think they are utterly miserable, but they are definitely less happy and who wants their kids to be just "fine", anyway?! It's frustrating sometimes as a feel we can't have a proper conversation with friends and family back home without sounding like we are being overly anxious. And yet these are people who are already (understandably) agonising over secondary education for their kids in four years time. Somehow once you take your kids overseas they are expected just to get on with it! Sorry, that was a bit of a rant :)
Putting him up a grade is something that we initially dismissed, and I don't think it would be possible in the public school anyway. I think there might be a bit more flexibility in the private school, I will ask.
NoMore - the private school does claim to have more flexibility over teaching to individual need, which sounds great, but it is difficult to know the extent to which this happens in practice. 500 children per grade!!! OMG that is enormous, absolutely overwhelming!
Nickname/tomato - a year to settle - that is really interesting to hear. Definitely much longer than I think most people (without first hand experience) would expect. And interesting about the "gut feel" too - that is exactly what I am trying to figure out. The fact that we don't see their teachers or other parents at the school gate definitely makes it harder to gauge what is going on - unless you proactively ask there is no feedback whatsoever, and my kids don't provide any either, unless they are either really happy or really sad about something.
MrsTerry - I really do think the kids are experiencing a bit of culture shock. I thought they would be immune because of their (young) age, but it seems not.
JellyTip - we are definitely doing as you suggest and trying to make family time as exciting as possible. A lot of you mention the importance of friends - DS(8) seems to be doing ok and has a couple of friends in the neighbourhood who are in his class at school, and they play out after school which is great, and something he was never able to do back home. So that is a big plus for him I think. But I think he finds it tiring, because of the culture differences - like he is subconsciously working at it all the time. DD(5) I am more worried about - she had a couple of wonderful friendships back home, and has spoken forlornly about feeling lonely here. Unfortunately neither of them are at all sporty, which is a shame as that is such a great way to get involved in something out of school. We are pursuing other things though like cub scouts, guides etc.
Canyou - thank you for your thoughtful insight. As I said above, I do think there is a tendancy to dismiss the complexities of what our kids experience when we move them. Just recognisning that is a good thing I guess.
naturalbaby - if the kids were loving their current school, like you I wouldn't be stressing too much about them catching up one way or another when the time comes to go home. But as they themselves seem to feel that they are getting behind, I feel like I should do something.
So the latest is - if anyone is still with me, sorry this is long! - we went to have another look at the private school yesterday and had along chat with the head. I can see in some ways it might well be a better fit for our kids, but I'm not so overwhelmingly convinced that the significant expense and additional disruption will be worth while. But what I was really pleased about it that they are happy for the kids to come and spend some time at the school and shadow the lessons. So we are going to give our DS(8) the opportunity and, pretty much, let him decide. With DD(5) it is harder as I don't think she can make a decision alone, she's too young. We'll have to see how that plays out a bit more I think. I'll keep you posted!