A couple of thoughts on this to share with you -
What was the difference between his daycare and this K class - was the size different? How are the teachers different? How is the classroom different and how is it structured out? These are key bits of information for you.
I think that your child, if this hasn't been a problem before, is having trouble adjusting. Some teachers are just not good a fit with certain childrens personality; some classrooms are not set up so they are comfortable for some children, but rather feel disorganized or overwhelming to a child; Sometimes there are too many kids and that feels overwhelming too. It's a whole new world and a lot to get used to.
Further - have you asked the teacher if there is any pattern to your son's behavior issues - is it just after recess, just before snack, etc... He could be tired or wired depending on what is going on - does your son need to eat pretty regularly? - could his blood sugar be dipping? - this happens to kids under stress too and if he is feeling overwhelmed, that will dip his blood sugar. Could he be tired? Was he used to so much curriculum as in daycare? That's an adjustment in itself. Maybe he needs to be outside when he's stuck in a classroom and it's uncomfortable - he's just not used to it. How much time did he spend outside at daycare as compared to school?
What I am hearing this teacher tell you is a lot of "the problem" and not a lot of solutions, patterns, or insights. Did you find out what the personalities of the teachers are in this grade at your elementary school? Perhaps you need a better fit for your son. As you mentioned, he had no problem in daycare.
Further, you may want to get your son checked for sensory processing disorder - his behaviors sound similar to some of the characteristics of this disorder - which is because some kids are uncomfortable in certain situations and have difficulty learning adaptations to such discomfort. The school system can test him for this and anything else. Much of lower level disorders come out in a childs first year of schooling. It's best to find out now and help him - if you do not, he will have learning disabilities eventually.
I would just talk with your son - I would not punish him since that is not working. There are so many other reasons - other than naughty behavior, that could be going on here. Start asking questions to get to the bottom of it.
Good luck -
Alli