Well I've written on her before about the problems I have giving the correct response when my son hurts someone (pinching usually- hasn't happened a lot- and generally goes for adults- no children).
At 5 years old he should know not to scratch, he should also be able to dress himself, wipe his bum, talk, play, apologise to other kids, say hello, feed himself etc but he can't.
He has had 2 episodes of scratching, first lasted 2 weeks, second lasted one week- the reason that we managed to contain it is because a very consistent reposnse was given to the behaviour. The toruble is the response that has to be given has to be neutral- a very calm response- where he is turned away and we put our back to him. Shouting, jumping around demanding apolgies all goes totally over his head- and makes it more likely to lead to another scratch "oh look how interesting everyone is being today". In fact it was my MIL who escalated the behaviour in the first place by stomping around and shouting and yelping in response to being pinched.
Often this sort of behaviour is difficult to stop- and the only reaosn I was able to do it is because as soon as it started I had people I could discuss strategies with- and we could then put in place a consistent strategy.
The toruble is despite him being non-verbal and classed for govt purposes as severely disabled, no-one actually notices as he looks normal so we get the dirties for giving the "wrong" response.
My friend's son has been biting for about 18 months now- he has something undiagnosed going on- and she has tried everything and had a lot of professional support. She still had to take him out of various playgroups etc though. One thig the behaviour support team said- which I thought was very sensible is that adults tend to see biting as being somthing much much worse than say pushing. But to a child they're just the same- they don't distinguish between them and don't realise that biting is more aggressive- they just want the toy.