I was recently told an anecdote about some high school gangs in California whose aggression towards each other finally resulted in them all being given anti-racist counselling by their teachers. It might be apocryphal, but in any case...
School pupils are denied the right to freedom of association. They are forced to spend time in close quarters with an artificial cross section of the population (ie other people the same age). It is a completely understandable response in such a situation to protect oneself from intimidation by forming cliques or gangs. Frankly, I doubt whether the colour of the skin is really such a big deal. If it was an all-white area, the gangs would have been preppies vs goths. Or mods vs punks, just to choose a random example from 1970s Britain.
I don't excuse gang violence. But responding to it with anti-racist training? puhlease.
If you are engaged in something constructive, you evaluate the people around you in terms of their value to the project, not the colour of their skin.
The best solution would be to stop locking children up in schools all day. Help them find constructive things to do rather than spending years trying to make them docilely accept being bored by "education".