I concur with the above post from specialmom, and yes be your childs advocate, I feel the teachers/school have been unable or unwilling to cope with your child,what is his behavior like at home ,have you problems with him when he is with you.
Hi, I am very sorry to hear of the difficulty you are having with your son. It is so hard when things like this happen---- my son had some issues in preschool and was later diagnosed with sensory integration/ processing disorder which is a neurological developmental delay. My son is very smart but his nervous system is off and if looks like bad behavior to others. School is where it is the worst. Anyway, he is now 5 and after occupational therapy is doing much much better.
What country do you live in? I'm guessing the US. We have laws protecting our children and their education in the public school system. Is this a public school system. Private is a whole other issues and they can indeed turn someone away. The school seemed to be going along the usual lines with your son that a public school system does--- identify a problem, talk to parents, recommend school eval, etc. They come up with a plan to help your child's behavior and learn their curriculem. If a child's behavior is so disruptive or abusive to the other kids in class, they will remove a child from class. They do have to protect all kids and their ability to learn too. So, I imagine they will work with your son---- but have issues until a plan (IEP, they are called) is set into place. Perhaps an aid in the classroom would help. If you are at a private school, you may need to go into the pubic school system. They are REQUIRED to provide services to help children in school. private is not and often don't have the resources to do it anyway.
As far as pills, I would want a diagnosis by someone qualified as a specialist in assessing kids. My son has sensory integration disorder which can look like ADHD but is not---- pills would do him no good and they have side effects. If your son does have ADHD--- pills can help (although they aren't magic). Good luck and it is hard figuring out what is going on with a child. He is probably very uncomfortable on the inside and acting out because of it. Poor guy. Be his advocate, stick up for him and be strong.