Wanted to add that the bad rap of tracking IMO results from times and or places (Germany is one to this day) that put all the low ability kids in a separate school which then ends up concentrating all kids from risk situations, from low SES backgrounds, with parents living in poverty or being unemployed or uneducated, and second language learner and kids with mild learning disabilities and with major behavioral problems, every one else trying to get the hell out of those schools and make it into the medium ability schools. I think those kinds of schools concentrating a high risk population shouldn't exist, and they have been proven to make every kid even worse of than the would be, the concentration of risk factors obliterating any benefit the targeted instruction might bring.
But won't parents who are able to avoid sending their children to schools with lots of at-risk children? Germany has separate schools based on ability. The U.S. segregates based on house prices.
Yes, of course that is what parents do, and they exert political pressure to water down requirements at the high ability (I really should call lit high achievement, there is no testing, but the decision is made either on fourth grade GPA or the teachers gut feeling or both). The pressure has resulted in some states high achievement track schools ending up with 60% of the age cohort and the low achievement track with 10 to 15%, with low track teachers complaining that education at these schools has become impossible.
It also has to be noted that the students in states who have mostly resisted that pressure and kept up rigorous entrance requirements by GPA so that the distribution is still pretty much equal thirds have achieved results in standardized tests (forced on them mostly by international surveys such as the OECD's PISA, they simply didn't exist before) that place them ahead of the students in "softer" states by about two years (controlled for ability, so it must be the instruction).
The tests have also shown though that the more rigorous the entrance requirements, the stronger the correlation with SES, in the "soft" states with the large percentages in hi achievement track it virtually disappears for those tracks (I am sure there is a perfect correlation with the low achievement track intake, though.
But parents do not push for entry into high achievement track for the high educational standards - you should hear the whining. They want the prestige, they want their kids to stay away from the riff raff, but they don't want the pressure if the kids having to work for it.
And now the political pressure is on to do away with tracks once and for all, because of equity, with differentiation provided by peer tutoring.
It's all very frustrating if you have a gifted high achiever.