Yes, I understand the concerns. It's the typical prisoners-and-guards problem - but the difference is that the teachers and pupils are not equals. The teachers are trained (albeit one of the points the inquiry mentions is that they don't feel the training is adequate), the teachers should feel a 'duty of care' towards the pupils greater than that of 'normal' children.

The other side of it is that because the punishment mechanism is fixed, and supposedly not influenceable by the teacher, there is less chance for the actual punishments to vary - only the circumstances under which they are given.

In order to balance that, there are also many checks and balances supposedly in place: guidelines, authorisation to administer the shocks, CCTV, etc.

I guess in the end it comes down to whether you think the means is worth the end result: the pupils in nearly all cases are able to have a better quality of life.