But how, in the heat of the moment, can a teacher distinguish between the reasonable and unreasonable? In most cases it is obvious, but not to everyone, it seems.
Some teachers have not been able to resist putting sticky tape over the mouth of a loudmouthed seven-year-old, or shutting an unruly girl in a cupboard, or cutting off the hair of a long-haired, anti-establishment teenager. The price can be both a prosecution and disciplining by employers.
But what is the situation if you grab hold of a pupil who is running down the corridor against the school rules?
It depends on whether a reasonable person would think that your prompt action was preventing the pupil from being hurt or hurting others, or whether you were intent on punishing the child.
Teachers and support staff have to be measured in their approach, even in the heat of the moment. If you walk into a classroom and see Wayne and Shane holding Duane by the arms and legs, about to launch him through the window, you are likely to act quickly, grab hold of Wayne and Shane and thrust them apart, allowing Duane to subside gently to the floor. At this point you have committed no crime. But the moment you bang Wayne and Shane's heads together shouting, "And don't do that again!", you have moved from justifiable restraint to corporal punishment.
If you are still uncertain, take heart from the music teacher who rugby tackled a boy attempting to leave his lesson declaring that he had had enough of being bored. The judge thought the teacher's tackle both effective and justified.
Chris Lowe, Chief editor, Quick Guide Publishing, and a former headteacher.