NO matter how naughty your son is, what the teacher did is totally wrong.
The teacher give him a negative feeling of school so maybe your son will dislike school.
Most of the time a kid around 4 likes to explore everything and which is not a bad thing,
only maybe in a wrong time. If you sit in your son's place, what do you think ?
Your son is so little the teacher only need to explain what's wrong. He punished him in front of everyone
which cause your son cannot face to other kids later.
If I were you, I will talk to school face by face.
wht naughty things that ur son has done? Is it really a big matter? If ur son really did sth worng, I would not complain to the school. Otherwise, I would talk to the principle and make he/she face the problem