Welcome!
You've received great advice above.
I'll just add a response to this part of your post...
In the instance with the preschool, he told us that they were hitting and pinching him, I think to try to control him.
Hitting and pinching would be "corporal punishment" and are not acceptable forms of discipline. There are a host of reasons why corporal punishment is not OK, including being a negative role model, essentially encouraging a child to emulate this behavior.
Please do the following:
1) Make careful notes at home. Ask your child gently probing questions to learn Who-What-Where-When-Why-How regarding the hitting and/or pinching. Are there any marks on your child? Any witnesses? Write down all the facts, according to your child's account. Make a copy and keep it at home, in a safe place.
2) Check your State laws online to see if there is any mention of corporal punishment as a form of discipline in schools.
3) Check your preschool website and/or marketing materials, application forms, agreements, parent handbook, etc, for any mention of disciplinary policies.
4) Talk calmly to the head of your preschool:
4a)Present the facts (#1 above) as you understand them to be.
4b)Calmly state that hitting or pinching your child as a form of discipline is not OK.
4c) Ask to hear the teacher's account of the situation(s). Ask when you can expect to receive this information.
4d) Be prepared to take notes on what they say.
There may be awkward pauses in the conversation. Do not attempt to fill them. Keep focused and on-topic.
4e) Thank them, leave politely.
5) After the meeting, send a polite e-mail thanking the head of the preschool for his/her time in meeting with you, and stating that you look forward to hearing the preschool teacher's account of the events of MM/DD/YY (and MM/DD/YY) by MM/DD/YY.
