'A common threshold' - this is false. There's no such 'common threshold'.
There's far far too much ambiguity and selection issues in IQ for us to use it reliably for that much in the real world.
Kids from poorer area have much less good parenting, their vocabulary is as small as 1/3 of those of richer kids entering Kindergarten.
From K-10 at least, it's probably a good idea to just teach kids, at the later high school grades, offer accelerated learning classes to whoever wants to enrol.
There's far far too much ambiguity and selection issues in IQ for us to use it reliably for that much in the real world.
Kids from poorer area have much less good parenting, their vocabulary is as small as 1/3 of those of richer kids entering Kindergarten.
From K-10 at least, it's probably a good idea to just teach kids, at the later high school grades, offer accelerated learning classes to whoever wants to enrol.