Streaming by ability wouldn't solve that. To illustrate why, I am reminded of a quote by Stephen Hawking;

“The prevailing attitude at Oxford at that time was very anti-work. You were supposed to either be brilliant without effort or accept your limitations and get a fourth-class degree. To work hard to get a better class of degree was the mark of a ‘grey man’, the worst epithet in the Oxford vocabulary.”

You could stream by behavioural attributes to achieve that if you wanted, but then you would have to accept that the classes would be very wide in ability, unless you stream by both behaviour and ability and then end up with a massive logistical nightmare.