Just to reassure those who will have children at upper schools, the top stream at our local upper school are pushed and encouraged
Ditto. In the part of Bucks where I live there aren't any Comprehensives, but interestingly the GS doesn't set for the first 2 years whereas the upper school does. The top sets at the upper school are most definitely pushed and encouraged – for example, extra classes were laid on for those who wanted to ensure they had covered the A* topics in GCSE maths. Those who got As or better in Y10 do further maths in Y11. The opportunities are there for those who want to take them, though admittedly they might have to show a little more initiative and self-motivation than is necessary at a GS.
We all compare ourselves with our peers and if the peers are only interested in make-up, boys and becoming a pop star then that is what our DC's will want to become. Follow the crowd and all that.
Anyone who thinks this only happens at an upper school or a Comprehensive is, I fear, going to be in for a rude awakening. Following the crowd happens just as much at GSs as it does at any other school. Better to show a child ways of dealing with this than try to avoid the issue.