My son is almost 2 and had the same problem adjusting to day care in the beginning. However, he quickly adjusted.
The fact that your son is throwing objects at the teacher and students might suggest there's something else going on besides problems adjusting to day care. I've always thought that children acting out is a way of telling people there's something wrong but they don't know how exactly to communicate it. It may be emotional or physical, which is why I wouldn't recommend punishment. It's tough, I know what you're going through. My daughter was the same way and it can get frustrating. We didn't know what to do. In time, she out grew it. Perhaps you can talk to your pediatrician or a child psychologist. It may also be the day care. Have you considered switching? My daughter would not adjust to the very first day care she attended but when we switched her, she did much better.
Good luck to you!
Where is he when he is suspended from school?
Have there been any changes in your son's life lately? New child in his classroom or new teacher? New medication? New weekend sitter? Just wondering if something could be upsetting him that's causing him to act out more so lately.
When my son was 4, he was in a Montessori pre-school program part-time for one semester. I told them that he doesn't have to be there and if he's having a bad day, I'll come and get him. They totally took advantage of that and it didn't take him long to figure out that behaving badly results in leaving the school and being with me. The last day I took him there, I didn't get two blocks from the building before my cell phone rang, telling me that he cleared another child's work off a table. I'm telling you this because your son may be connecting/associating bad behavior with not having to go to daycare.
Also, if my son had a good half-day there, we'd go to the park, McDonald's Playplace, Chuck E Cheese's, bowling, swimming, etc. If I had to pick him up early, we went home. He wasn't punished or made to go to his room, we just didn't do anything special (and he definitely realized the difference and I would reinforce that when he asked me if we were going somewhere fun). His teacher tried to get me to punish/discipline him at home, but while I would reinforce their rules (be kind and gentle to others, keep your hands to yourself, only work on your own activities, etc.), I just felt that his consequences needed to be at school--not allowing him to go outside to play at 1 p.m. or sending him to bed early because he threw a puzzle on the floor at 9 a.m. didn't make sense to me.
If they can't figure out how to work with him, I would consider looking for another daycare. They should care about helping him and making it work since losing him would likely mean losing your other children, too.
Best of luck to you!