Hmm...they're not. I'm concerned about any child who is being hit by his teacher. My son says kids tell him to stop all the time. Honestly, the first time he hit my son my son blurted out, "What the hell?!" I mean, it really startled him. He said the teacher just laughed.
I just asked him if today was any different. He said no. In fact when Mr. X yelled something in class today, a student said "cut it out, man, that's stupid" and Mr. X replied,
"Your face is stupid."
Besides, I would think a teacher would automatically assume students did not want to be hit in the head from behind. Maybe it's just me.