Forgive me, because I keep posting this same message! In your case, your son is testing his boundaries at school, where the "discipline" method is different, and he knows it!
I keep HIGHLY recommending a video series on encouraging good behavior/managing difficult behavior, that can be bought or borrowed from libraries/school district resources. It is called 1-2-3 Magic by Dr. Thomas W. Phelan. Please just check it out. I used it at home and it worked perfectly! But when my 5 year old strong willed, intelligent child went to kindergarten, He suddenly began bullying there, right after I had the method mastered at home. So I spoke to his teacher and told her what I was using at home. I borrowed the videos from specifically...a woman who worked for our school district, associated with my sons school. Her title was an Early Intervention Specialist from the Area Education Agency. The tape series has one for school teachers to use in their classroom. My sons teacher checked it out, in her spare time. And since then THE SCHOOL HAS IMPLEMENTED THE METHOD, in their classrooms, starting with her classroom!!!
Im not sure you will have the same luck or reception from your sons care facility...BUT, you COULD let them know what you do, that is effective at home, and see how they could try to duplicate that. Like a time out area for him. He could really feel how your rules apply everywhere. He is very young though, and he could just be mad inside, because he would rather spend the time at school, with his mommy.

I too have a 3 1/2 year old daughter who, to my knowledge, began hitting and kicking the other children at her learning center (again). She was acting out at her previous daycare and I attributed it to the lack of structure and discipline at that facility, but now she's in a much calmer and structured learning environment which I thought would help. However, it appears that she has taken on the role as the aggressor. She is put in time-out at school but as soon as her time is up, she does it again. I've spoken to my daughter about the incidents and the responses I get to my question - why did you hit so and so, are "because" and "the kids won't leave me alone." I asked her teacher if there was a problem with any of the children and she told me that these last two incidents my daughter initiated. She also indicated that during project time at the table she won't keep her hands off of the other children sitting next to her. I'm at a loss and feel like a failing parent because I don't understand what's going on with her. I sure could use some advice.
Thanks
Chris