I am a public school teacher in New York City. Every year we have an orientation on the topic of corporal punishment. It is given by an administrator in charge of security. The topic is: THERE IS ABSOLUTELY NO CORPORAL PUNISHMENT OF ANY KIND IN THE PUBLIC SCHOOL SYSTEM. It is simply not allowed. No spanking, no smacking, no raising your hand to make them flinch. I can NOT make them stand for a period of time because it can be interpreted as a corporal punishment. I can not belittle them verbally, becuase it can be considered as an emotional abuse. I cannot throw them out of the classroom. I cannot raise my voice as a method of instilling fear into the little darlings.
If your child is being physically punished in public school, you have every right to call the police. The only time when the force is allowed is when a member of the security team restrains the child to prevent him from harming others and himself.