I am unaware of any country that makes a significant effort to tailor instruction to very high ability students in any systematic way. This certainly doesn't occur during primary school age anywhere in the Anglosphere.

I'm also not bullish on the positive effects of primary school on cognitive skills full stop. Unschooled children are only a year behind their counterparts in public schools on average. That's a really small effect for the difference between more than five hours a day of purposeful instruction versus none whatsoever. The same study does show children in structured homeschool doing one to five grade levels better depending on what's tested so there almost certainly are students who benefit from earlier more advanced reading instruction but the implications for mass schooling are unclear. If we can't even have children in different classes by ability level instead of age group I don't hold out much hope for sane educational policy.

The Impact of Schooling on Academic Achievement: Evidence From Homeschooled and Traditionally Schooled Students