There can be bad teachers...
There are probably a higher percentage of Bad Parents though...
Not disagreeing.
However, I still don't believe a TEACHER should be responsible for handing out punishments. If a child is disobedient (or as you said "doesn't have manners"), send them to the office, call the parent, and come up with a solution to the PARENT'S DISCRETION (as far as corporal punishment goes). If the parent disagrees with corporal punishment then there are much more productive forms of discipline.