There are some moments when children become very agitated and difficult to manage. Often, these moments are triggered by the anxiety of the parents who, at the mercy of the situation, act in the hope of having some effect, which often does not happen. But what is happening? Maybe you haven’t noticed but the child has been overwhelmed by stimuli and what you see is a meltdown, that is a real “overflow” of his arousal. You have to know that every child has its own activation and that every child has a sort of cup in which all the stimuli, he has to manage, are inserted. A child can have a smaller cup and another child a larger cup, and this will determine how large its capacity will be. The right arousal or the right activation is, as the ancient Greeks told us, in the “metriotes”, the right medium. If the cup is not sufficiently full, the activation will not be sufficient but if it is too full we will have the opposite effect. What was it that de-weeded the child? What was he overwhelmed by? Especially the meltdown is not a problem behavior.
Meltdown is a clear signal that the child needs, first of all, to decrease sensory stimuli and
restore some quiet to his brain. Now let’s pretend we’re in class.
Maybe the teacher made a lot of requests together, maybe the class was particularly noisy, maybe the songs heard during the music class had annoying bass notes. The child in meltdown passes his “self-control” point, and if you keep talking to the child, as if that was a voluntary reaction, you will only make the situation worse. There are top-down and bottom-up thought processes, this is part of the second one because it is a response to sensory overload.
Just to emphasize the neurological rather than behavioral aspect I add a clarification.
The autonomic nervous system is so called because it regulates the activities in our organs that are not directly under our will.

This system is divided into two components with opposite effects: the sympathetic system which intervenes in situations of “danger” and the parasympathetic system which “modulates” and brings back to a situation of calm. The two systems have to maintain a sort of homeostasis but, in these precise situations, the sympathetic system has the upper hand, causing an Attack/Escape or “freezing” reaction. The environment therefore becomes potentially dangerous, stress increases and the child begins to function completely dominated by the sympathetic system. His vagus nerve goes completely on tilt, the child is in full production of cortisol and adrenaline.
The best thing to do in these situations is to accompany the child to a safe area or, if you are in class, invite children to be quiet and explain that it is important for their companion. Then reduce the stimuli and stay close to him or her, leaving him or her at a safe distance. Evaluate the breath, the pupil, the sweat and when you realize that he is “lowering” invite him to take deep breaths, slowly you will see that he will become more present.

A meltdown is not punished and not sent to extinction, a meltdown must be managed starting from the awareness that there is nothing voluntary on the part of our child.