Bit reactionary to report an 11 year old even if he did say arms I would have thought? Obviously don't agree with the teachers actions (surely she should have asked him to clarify what he meant first?) but I could see why she might have heard arms, alms is a strange choice of words, it's a pretty old fashioned kind of a word to use
I think the only time I've ever heard that word used was in Robinhood Prince of Thieves