To add to what fembear has said...
kittybrown, assume that there is a fool proof way of identifying the top 10% in intelligence. Wouldn't that set include all academically gifted children?
So the problem is with the identification?
On the face of it, IQ tests appear to be the more logical solution ...if the only option was achievement based (which it is not).
However, there's are several problems with IQ Tests. Apart from being highly unreliable at lower ages, each test needs to be conducted by a properly trained psychologist. The resources that would drain from the system would be huge. What guarantees would there be that these psychologists are independent? We've seen how the establishment fails brighter kids. The government's own reviews are scathing. Teachers - and G&T coordinators - openly state that they pay the scheme only lip service. Why would new employees in that same establishment work contrary to what their colleagues are trying to achieve? Even if IQ testing is done fairly it's going to spot very, very little of the real geniuses. Everything from photographic memories to exceptional talent in art, sport and music would be missed.
I think the current, multi-pronged guidance is quite good. That it's not successful is in no small part due to those teachers who are happy to take the job (and pay?) of G&T coordinator but lack the conviction or decency to declare that their moral opposition to G&T directs them only to sabotage the whole concept of finding talent and catering/nuturing it. Their resentment and malevolence is directly particularly at catering for the academically gifted.
You've got to be careful with criticism of the G&T. Die hard socialist absolutism motivates some to hijack any criticism as an argument against any specialist provision for the more able. They see it as elitist, as unfair, as entrenching advantage. They clutch at any straw. That there is an occasional pushy parent is seen as just cause for banning completely not just provision for the more able but even the identification of the really gifted. That the initial filtering is a broad 10% is used to argue that no really gifted children exist.
Differentiation should happen across the board, yes, but there are sometimes children so gifted or talented that they are off the scale. For them the normal differentiation is just not enough. A child may have exceptional gifts in music, art, a sport or an academic area that is just beyond the teacher to cater for adequately. I have a 6-7 year old DS who can do stuff with numbers that none of his teachers can. He has a million maths questions that his teacher can't even understand let alone explain. Differentiation in his context is doing a different sheet of work ... not helping him enjoy and explore the subject. It means keeping up an appearance of teaching him instead of actually feeding his appetite for knowledge.
Encouraging such children to meander towards mediocrity may create less work for the teacher/school but is shortsighted, stinks of envy and, to me, is deeply repugnant. Society is all the poorer for it.