However, I define gifted something like Mensa defines a member: an intelligence score around the 98th percentile or so.
So this is what I think happens, we mentally gather together all the people who make the cut off with an IQ test, and ask ourselves, who else 'fits' more with this group than with the default group? Then we ask, who else, if give thoughtful accommodations, would also fit better with this group in one domain, or in multiple domains?
My favorite example is algebra - it's hard for a 7 year olds chubby hands to do algebra, but given a work around for that, the gifted 7 year olds would enjoy it, (at least once the emotional block from enforced underachievement have been overcome)while regular 7 year olds would have neither the interest nor the ability.
So my favorite way to identify gifted kids would be to offer kids chances to participate in meaningful learning opportunities well above what is expected for their age level and see who thrives. Quantifiable? Perhaps we could have kids fill out a form after the experiences noting their level of interest and happiness.
My son thought for a while that the best way would be to ask kids, under lie detector situations, if school was too hard or too easy and which grade they belonged in.
It's also been studied just asking kids in the classroom - who is the smartest boy? who is the smartest girl? Or - which children here need more chances to learn hard stuff? It works quite well. There is an 'it' which IQ tests measure quite well (although far from perfectly) and as humans we know it when we see it in our peers. Except our really quiet or buttoned-up peers perhaps. We gravitate towards people who get our jokes, which depends on shared context, some of that context is all about intelligence.
One thing, I find interesting about 2E is that as the ansynchrony gets larger, it shades into 2E. If a child is ready to discuss college level books at age 9, what are the odds that they are also ready to write 30 page papers about them? Which part of the child do we address, which their mind is craving for, or what their organizational skills allow? And it isn't that discussing books is easier than writing about them. There are plenty of kids who can churn out the long papers efficiently but with superficial levels of thought, but can't follow that deeper level of thought in the discussion. And can you actually teach that kid to write 3 paragraph essays on Dick and Jane books? Maybe, Maybe not.
Shrugs and More Shrugs,
Grinity
