I'm going to make a statement of fact which isn't racist, but factual.
Of the 14 secondaries that converge at the clock tower of an afternoon, co-ed, single sex, grammar, sec mod and comprehensive, the only school that is a re-enactment of Beirut is the Catholic boys school (and I've worked there too). It has race wars (black on white, black on black) high levels of immigrant population. The pupils travel far and wide looking for "victims", out of borough as well. It is continually in the press, generally for stabbings, frequently fatal. Massive drug problem too.
The whole area naturally evaporates of shoppers between 2 and 4 because of their behaviour and is awash with police. All the other school mix in quite happily, waiting for their buses, catching up with mates from primary school and so forth so where this whole 'grammar kids get their heads kicked in' comes from, I don't see it.
The Catholic Boys School was one of the most frightening places I've ever worked. 14yo's my arse, might have been getting access to the UK on the passport of a 14yo, but there were a lot who were clearly in their late teens and early 20's with a hell of a lot of 'tribal' baggage. You try getting between three alleged 14yo's going at it hammer and tongs in their home tongue, who then round on you because you are a woman, white and therefore a piece of shit in their eyes.
www.newsshopper.co.uk/news/8783689.BEXLEYHEATH__St_Columba_s_school__extremely_shocked__at_stabbing/
and more high profile case
www.guardian.co.uk/uk/2011/jul/03/yemurai-kanyangarara-london-stabbing-murder
Went a bit tangent there. So uniform has it's place if only to ID murderers.