I think it completely depends on what has happened. Quite often schools impose a temporary exclusion while they investigate and then make a decision about permanent exclusion. That would normally mean that they must make a decision before the temporary exclusion comes to an end. If they're not doing a temporary exclusion, I'd have thought they need to make a decision pretty quickly, because the longer they take about it with the child in school the more difficult it is for them to argue that they can't have the child there.
Does anyone know what an average investigation time would be before the HT decides to permanently exclude a child? I understood that there should be a thorough investigation with reports written - is this usually the case? Thanks.