Wow. There is a huge amount of misinformation going about on this thread.
Just to clarify- ANY teacher can restrain a child, in ANY school; not just PRUs/SEN/EBD schools.
Teachers- ALL teachers- have had the power to restrain children for years- in fact, by doing nothing, ie not physically intervening in a fight, or fetching somebody who is willing to physically intervene, you can be sued for negligence. Any 'no touch policy' is erroneous, and leaves children vulnerable and staff at risk of litigation and dismissal.
In the OP's case, had her son run into the road, the teacher could have been sued for negligence for having done nothing to stop him.
I am a teacher, and train other teachers in positive handling (restraint). I have taught in mainstream, SN and EBD settings. The problems arise when teachers are not properly trained to physically intervene- not only do they not know how, but do not know when it is appropriate to do so; and when it's not. Is it appropriate to physically prevent a child leaving a classroom? Sometimes, yes. If they are going after another child to beat them up for example. If you believe they will harm themselves or others, then yes. Because they didn't follow your instruction, then no. Deal with it later.
The legislation needs to be clarified. Presently, a teacher can restrain a pupil if:
-A child is injuring others
-A child is injuring themselves
-A child is damaging property
-A child is behaving in a way that is likely to disrupt good order.
Any physical intervention taken must be reasonable, proportionate and necessary.
This means that if a pupil is charging at another holding a knife, you are justified in rugby tackling them to the ground- if they are verbally abusing you, you are not.
The vague definitions do not help- 'damaging property' could mean smashing a window; it could also mean snapping a pencil in two. Legally, you could restrain a child for this, but ethically? It would be completely inappropriate. The legislation relies on teachers' judgements of what is reasonable, proportionate and necessary, and there is rarely any provision to train them to effectively make that kind of decision.
As a teacher, you have a duty of care to keep children safe, and act in loco parentis.
This does not mean that you are required to restrain a child, but that you cannot do nothing. Even fetching someone else to help is something.
Sorry to waffle on, but am staggered by the number of posters who think that teachers legally cannot restrain children- not having a go; many teachers think this too, but it is incorrect.
OP- YANBU. The teacher had a legal duty to help prevent your son from endangering himself- even if that involved getting someone else to help. Doing nothing is negligent.