The teacher should not have done it and although I don't feel it justifies dismissal, I suspect that's what will happen. Formal reprimand and intensive training re classroom management would be more appropriate imo.
I reckon this story is also massively exaggerated, my ds complained about being 'shut in a cupboard' at school, after detailed questioning it transpired it was a small room because he hadn't finished his work - so children do exaggerate.
The press have totally spun this to the max. It saddens me. Daniella Westbrook speaking on the Wright stuff is also 'outraged' about this 'abuse' she is ridiculous.
Generally I am troubled by parents being constantly 'outraged' by schools attempting to discipline their children. They are paraded in the press with arms folded and wearing angry faces. This is usually about uniforms ie the unfairness ugg boots not being allowed school.
Parents should work with the school and if there's an issue deal with it through the right channels not ring the press.
They will be suing without a doubt.