Some kids might get spanked or beaten at home; others may have parents who don't believe in corporal punishment and strictly avoid ever laying a hand on their children in punishment. How would you treat these children in school if corporal punishment were permitted? Spank them both or only spank the ones who get it at home too?
What if you knew that the particular child has never been spanked or beaten before because his parents don't believe in it and would be severely emotionally traumatized if you spanked him in school? Do you still do it, or do you avoid it in that case?
How can you justify different treatment for the same misbehavior?
Should corporal punishment ever be administered in anger by the teacher?
How do you police it so that no teacher ever administers corporal punishment in anger?
Should corporal punishment be justified if it leaves any scars or bruises on the child? How do you police it so that bruising and scars never happen, since the sensitivity of kids' skin differs from kid to kid? How can a teacher know in advance which kid is more sensitive to bruising and broken bones and should not be hit?
What if a kid is a foreign student and comes from a culture or country that abhors corporal punishment? Would you still force that child to be punished by corporal punishment?