When a pupil is highly emotional, their thinking brain is offline. Asking them to 'calm down', 'explain themselves', or 'apologise right now' is asking for something they literally cannot do in that moment. Trying to reason with anger fuels it.
Three principles guide de-escalation. First, lower the stimulation: drop your voice (don't raise it), reduce eye contact slightly, give physical space, and ask other pupils to look away or carry on with work. Second, validate feelings without endorsing behaviour ('I can see you're upset; I want to help' — not 'you have every right to throw a chair'). Third, give the pupil a face-saving exit ('go to the cool-down room and we'll talk in 10 minutes' rather than 'you're in detention now').