It's a big deal when you send them off for the first time. I found it hard to not be aware of everything they did and I didn't get a full report about their day like I did with the daycare. HOWEVER, it is them growing up and learning to be independent. I don't know if it has anything to do with being a preemie though. I've met quite a few parents whose children are in school with mine and some of them are totally over the top in my opinion. I know their kids weren't preemies. The twins went to overnight camp for 6 days this past summer and I was a wreck, but I know it's important to their sense of independence to be able to do thing for themselves. I knew the camp director and I drafted emails every day and then had to force myself NOT to send them. If there was a problem, they would get in touch with me. It was hard though.
There's been a lot in the media about the kids in high school not being able to think independently since their lives have been scheduled from the moment they woke up and were driven to school until all after school activities were done and they were picked up and driven home at night. These kids are going to university and don't know how to act by themselves.
I do think preemie parents have a different appreciation for things their kids do, since many of us had to wonder if they would live or if they would have long term developmental issues. Are they more attached? not sure about that one. I think it may be harder to accept at some point that your child no longer needs special attention due to the prematurity.
Wow, I didn't realize I had so many thoughts about the subject. Sorry for the rant, but you asked:) I would suggest a deep breath, lots of talk to the teacher, maybe in a few weeks, volunteer at school if the teacher doesn't think it would affect him. Remember, he's been through so much more already and is stronger than anyone thought!