I agree Seeker.
I think that these gifted children disappear at some point between the age of 4 and 18.
When I was at primary school (all three of them state schools) there was a thing for putting bright children up a year.
However, when I got to Cambridge, I never met a single student who had been put up a year or labelled gifted. Where had they all gone? The brightest student I knew (top every year in Physics) was so bright that no teacher could have stretched him (with the possible exception of Einstein).
With respect to all these children who need to be stretched...I wouldn't want any child to be bored at school. However, I think that a bit of cruising, in a mediocre environment isn't as bad as people think...
It's only primary education after all! And, storming ahead at the age of 7 doesn't mean that you are going to be able to cope with degree level maths at an 'elite' university.
I think that most academic achievement comes from self motivation and whether your brain is bright enough, not whether you are in a class of 30 of 18.
So, private education definitely not worth it! Save the money for holidays and enjoying your children. (That's if you ever see them between violin lessons, ballet, swimming and Kumon maths).
Gosh, I'm so cynical...but I just enjoy watching my children play and learning from their play. I believe the more I let them play now, the more they will be able to develop their own learning desires and abilities.