Why would school be protecting a bully?

[Firocoda]

DS11 and several other boys in his year at boarding school have been repeatedly "bullied" (although school says it isn't bullying, "just" verbal and physical aggression) by a boy in their year. This has been going on for two years or so, since they started at school. Parents and boys have all complained, repeatedly. The school is getting a complaint at least every two weeks about this boy. He's hitting, kicking, violent against property, biting, yelling, threatening to kill people, etc.

Supposedly the school is taking action. The boy is in clear violation of the school rules and could under these rules easily be expelled. Apparently there's more going on than meets the eye. What could possibly prevent an independent school from expelling a child like this? He's not well-connected or anything. I suspect that there is some sort of legal protection in place because he has some sort of diagnosis?
I'm just trying to figure out what's going on here.

It doesn't sound like bullying from OP, as there is no consistent picking on one or more victims.

The school would be in the wrong if they disclosed information about what they are to third parties, including other parents, though you could ask about steps in relation to incidents directly involving your DCs.

It all comes down to whether you trust the school to be acting appropriately and effectively. If you don't, then you need to ask yourself if you can trust them on anything, and if you don't then consider if you should move your DC to a school you can trust.

1. The boy could be responding in extreme ways to being bullied himself -remember if this is a boarding school I assume you haven't actually witnessed the behaviour. He may be a boy that others wind up and then cry 'bullying' when he overreacts aggressively.

1. Boarders fees are valuable to the school, in my experience it's takes A LOT for a boarder to be expelled.

1. Bullying is a sustained campaign on an individual it sounds as though this boy is hitting out at ALL the boys around him. This speaks of a boy with problems, is it possible his fees are paid by grandparents/the state/someone else and he is being kept away from an extreme home environment- are the school trying to give the boy a better chance- if so it will probably take more than one school year to 'fix' him.

1. They are building an evidence file but being quite 'lawsuit aware' (have they been sued in recent memory?) they are quite risk adverse and it will take time.

1. They are actually a bit shit, in which case why are you sending your son there?

DS has started to stand up to this boy (I got him help on how to do this), but there's another boy who won't, and he keeps getting picked on by this boy. Apparently now there are two other boys who are getting picked on as well. I see DS 2 or 3 times a week and speak regularly with the other parents, so I am quite sure this boy isn't being bullied. I think that Sarcalogos' points #3 and #4 are right. Is it more difficult for a school to expel a child if he's statemented or similar? Or would the school not be allowed to expel a child if the home environment were horrible?
Ordinarily I (and the other parents I think) would be removing our boys from this, but it's a particular type of boarding school, which makes it more difficult (can't say more for fear of outing it).

If it is a state boarding school, yes it may be difficult (not impossible) to expel a statemented child.

There are a reasonable number of children in care in state boarding schools. Now while the school can get rid, it is likely that they will try their upmost to support the child (through a desire to help them), before going down the expulsion route.

If not, it's highly unlikely that the boy even has a statement, most independents encourage parents not to have a child statemented, but generally provide support in excess of what a statement would have offered. Independents can expel who they want (within reason) and are nowhere near as constrained as the state sector, though they have a greater reliance on fee money and are becoming increasingly risk adverse.

What could possibly prevent an independent school from expelling a child like this?

Money.

Doesn't stack up though, does it? Keep this one child, but lose two or three others (either immediately, or by choosing to leave at 13 rather than staying on as they might otherwise have done), whilst losing reputation amongst gossiping parents (who might tell others in frank and disobliging terms what they think is wrong with the school).

Depends on the area, I suppose. Maybe this school is the only independent school in an area where people are frightened away from state provision by tales of poor standards, drugs, bullying et cetera and are confident that parents won't vote with their feet?

It's either money or the bully is more well-connected than the OP thinks. Or, of course, the school are simply incompetent at managing situations like this.