> Can you provide any evidence that G&T programmes exacerbate weaknesses?

None at all other than anecdotal.

> Most school dsitricts don't have such programmes at all

This doesn't jive with my experience where literally every school I attended had some sort of program (and I attended quite a few schools growing up- more than grades). Often in single district areas too where it wasn't possible for my parents to have chosen the right school. A quick google search reveals 6% of schools are enrolled in the national gifted and talented program. Perhaps that is your definition? I imagine it is far too narrow a criteria and that plenty of schools offer special classes for a small minority of their students.

If 6% of schools have a G&T programme surely that proves a tiny minority of students are enrolled? It's not like honors or AP classes are targeted at top 10% or 5% students.

In my school district, not every school had a GT program; if your base school didn't have one, you'd be instead bused to the nearest GT program. You'll need to compare school districts or (better yet) student populations, rather than merely schools, to get a better estimate.

Thats the "official" G&T program statistic. I don't know anything about the requirements to be on that list, but perhaps it is onerous? My claim (unsupported) is there are plenty of schools that run G&T programs that are not on that list of 6% that, if counted, would raise the percent dramatically- perhaps to the 75% level? I don't know.

> My claim (unsupported) is there are plenty of schools that run G&T programs that are not on that list of 6% that, if counted, would raise the percent dramatically- perhaps to the 75% level?

Unless you count AP or honors programmes as G&T this isn't remotely close to being true.

> None at all other than anecdotal.

I doubt you even have anecdotal evidence.