..my posts are about corporal punishment in general, which is what I assumed was the intention of this thread. Still if my sensei slapped my face (which I can't picture him ever doing) I would talk to him about it...
Of course, and I agree wholeheartedly with the course of action you propose for the student in such a situation. The original question, however, was about justification of the corporal punishment. If we decide that it's a private matter that requires no justification, then there's nothing to argue about.
However, if we are talking about effectiveness and the value of corporal punishment, I maintain that in my opinion, use of corporal punishment reflects poorly on the sensei, showing his lack of consideration for the values of the society he/she teaches in.