Ideally, each child would have the right to be in a class room where the majority were within a standard deviation of the child's ability and majority middle class by SES, Not everyone! Which would give schools the possibility to not compose classes with majorities below 100 or living in poverty, both extremely unhealthy classroom environments for everyone. In the highest reaches of ability,the slices as it were could get thinner, with Hg+ classes at the top, necessitating some concentrating and travelling for these groups, but precluding the necessity to bother about whether concentration of high SES kids in these classrooms distorts the distribution for the other classrooms, as the critical mass of middle class kids will be reached regardless.
Sorry, somewhat OT, pet topic of mine.