Will I get sued if I publicly complain about school experience?

We sent our four year old son to a private Pre-K school last year and it started off fine but by the end of the year we were getting complaints from one of his teachers and an administrator about our son’s “aggressive behavior”. They said he had pushed kids on two occasions and even “bit” another kid once. Preschool behavior to us but they suggested we take him to see a psychologist because they thought there may be “something more serious” going on. They said “maybe he has sensory integration disorder or something”. We took him to a psychiatrist, a psychologist, and his pediatrician. They all said the same thing: “There’s absolutely nothing wrong with your son. He’s acting like a four year old boy. Move him to another school.” Before we made the decision to move to another school I observed my son in the classroom (from behind a one way mirror) for two hours. During that time he did not act aggressively or impulsively one single time. Further, the teacher told my wife that our son’s behavior caused the other kids in the classroom to not want to play with him. This caused us stress, but he had plenty of friends begging their parents to have playdates with him and when I observed him in the classroom, other kids were constantly trying to play with him. We became convinced the school was more committed to finding fault with our son that troubleshooting preschool behavior—so we moved him to another school. Three other parents also chose to move their children to other schools for similar reasons. The experience left us bitter and concerned for kids that would attend this school in the future.

I told the head of the school that I wanted a full refund for the school year, in part to ensure that our concerns about the schools training and approach to dealing with spirited children would be addressed. He decline to issue the refund and now I am wondering what I can do next, short of suing the school. Can I create a Facebook group for parents that had similar bad experiences? Can I complain to State Education Department authorities? Can I seek out other parents in the Pre-K program currently, as well as board members of this school, to share our treatment? Can I write as letter sharing our experience and publish it on a website/blog? Am I just exercising my rights to free speech or can it be considered harassment and extortion? Is it slander? Am I likely to be sued if I express myself? What else can I do?