What you said
Have you tried giving them the option of stepping outside for a moment to help them calm down? It works with some children. Sometimes they find themselves getting out of control and have no idea how to deal with it. If you can calmly give them a bit of space, this can be really helpful.
Children who refuse to leave are doing it for power reasons. If the teacher asks them to step outside for a word and they don't comply, the answer is to say to them that they have 30 seconds to leave and if they don't, then sadly the entire class will have to leave the room. You then take a back step, allow the miscreant to choose to leave (trust me, there will be a lot of irritated students who yell at him to do so) and in the 5 per cent of cases where the child still refuses to cooperate, you apologise to the class, throw in a few comments like, "Unfortunately Joe doesn't want to let you get on with your lesson," and get the whole class to go out of the room.
The expert view
There isn't a significantly better alternative to removal: it is necessary for the good of everyone, including the guilty party. In the first instance, ask the child to step outside, without showing anger; if you're aggressive, you'll encourage them to defy you to save face. If they refuse, send a trusted student, a classroom assistant or, if necessary, the teacher next door to summon a senior staff member. By that point, most students will realise that the situation is escalating and many will comply. Some won't, or will revel in the attention, in which case keep calm and try to carry on with the lesson until help arrives and the child is removed from the room. The key thing is to remain serene and not feed the child's desire for attention. Finally, make sure a sanction results from the event.
Tom Bennett's latest book, Teacher, is out now, published by Continuum.