Hello and welcome Amy,
You are lucky to have a diagnosis this young. I knew my son had problems by the time he was 3, but I didn't know what they were and his preschool teachers always brushed off my concerns, saying it was normal for kids this age to be impulsive and distractable. When we took him to a therapist she focused on our discipline and told us that he didn't listen and follow directions because he was ignoring us and he didn't want to.
If you are concerned about the ADHD not being addressed you should talk to both his teacher and the case worker. Let them know how much you appreciate the speech services, but that you are worried about the ADHD affecting his education. You will most likely be told that they need to wait and see if that's the case. But keep on top of it. In my experience the school administration would just like to "wait and see" until he's out of their school.
You will probably get your most valuable info from the teacher, as she's with him every day. Write down everything she tells you about his behavior in class. If you can, get her to email you updates about behavior and concerns so you have it in her words. I've found that you basically have to "make your case" to get help for this.
I also found that at this age 1-2-3 Magic worked well to get my son's behavior under control and using it along with reward charts for good behavior helped a great deal.
Hello. How much is the ADHD interfering with his learning? Since school just started, you don't know. See what his teacher says a week or two from now. He just started, and he may be adjusting to school. Do some research on this site and other places to see what you will need to do if you learn that indeed his ADHD is impacting his learning. Read some of the other threads too. I'm new here, and my impression is that there are a lot of very knowledgeable, understanding people who post here, with good insight.
IMHO, outside of impacting his learning and his safety (and that of the other kids), if the school doesn't think the ADHD is an issue, then they must be able to handle it, right? I think you know what I mean. Just make sure he's learning and that he's safe. Just my 2 cents. Good luck.