I think indigo's recommendation would work, or at least significantly improve education in the US, but politically it is very difficult due to the links between performance/SES/race.

DS has learned math primarily through independent study online and I wonder if accelerated kids could not have more of their learning via online resources enabling a higher teacher:student ratio, freeing up teachers to spend more time on kids that are not performing as they should. The disadvantage is that accelerated kids would have less teacher instruction but at least they would get more challenging material and be able to work at their own pace.