And sadly, still aren't. They can move the gifted kids into fast-track, but that still doesn't accomplish anything if your kid is a math whiz but struggles with reading, or the other way around. And No Kid Left Behind and Teaching To The Test makes it impossible for teachers to do anything but spend time on the ones who need help, while the ones who should be excelling are left bored and unchallenged.
I got a lot of "doesn't apply himself" back in the day because my teachers didn't understand that I already mastered the material the first time and tuned them out when they repeated it over and over to the kids who weren't. They called it "daydreaming." I called it imaging the cool stuff I could have been doing other than sitting there. At least I was allowed to work out of the sixth grade math book as a third grader because the teacher wanted to push me.
My father also brought home the IBM tutorial books used to train new computer programmers when I was 12, so I already understood bits, bytes, hardware, software and CPUs before getting to program in Fortran in ninth grade.
A really progressive school district would separate classes by subject right from kindergarten, just like in high school. Truly gifted kids need a different learning experience than what most public elementary schools offer.
That way, for example, you might be allowed to take fourth grade math as a second grader, even though you're technically not old enough. It would also allow kids having trouble to repeat a subject or two without having to be held back a full year. Yeah, I can see where parents might be bent out of shape about Johnny or Judy being pushed forward or back, but it would give teachers a chance to have everyone in their class basically at the same instructional age.
High schools offer AP and college credits but so much more could be done earlier.