[tomp]

Noone said that you need to forcefully segregate people based on ability. You don't even need to measure it!

Just offer different classes, with different difficulties. Some people will be bored and go to more advanced classes, others will struggle and move to less advanced classes.

There's actually a well-organised system that almost does this - primary school! Except that there, people are forcefully grouped by age, when there's really no need for that. That's (one of the reasons) why I advocate for mixed-age education.