Hi ZM,
I think I understand why the teacher made the comment about a mid-day visit being a setback; for kids who get upset at separation, having a second separation in the middle of the day is so hard for everyone. I did see this on more than one occasion last year when I volunteered at my son's school. (He did K last year). For the kids whose parents returned to further soothe the child later in the day, it was *always* the case that there were tears and upset during the visit or even after. Many kindergarteners would be upset if their parent came to volunteer because they didn't understand that the parent wasn't there for *just them*, but for the whole group. This is a *huge* shift in the child's perception of their parent, and while some kids do fine with it, for others, it's just a huge gap to bridge. Thus, they were upset if their parent showed any attention to any other kids and parting once again became something the teacher had to attend to. So,understand that this is another possible reason for him to be upset if you visit. And at the beginning of the year, this becomes even more difficult because the teachers are still learning the children's names and dealing with figuring out the interpersonal dynamics which happen at lunch/recess times. She's just trying to get the kids adjusted and to help contain emotions, period. Huge work.
So, I can see why she advised you not to come in for lunch right now. She wants to give him time to let him work things out on his own-- and he will feel so good when he does. Sometimes, giving children time to learn how to cope is the kinder thing we can do.
I also agree with having a note in the pocket, a "Kissing Hand"... some sort of ritual to help with separation. You don't want to give something so distracting that he doesn't pay attention to the teacher, but something that soothes. A felt heart or a little note "mommy loves you", something that's just for him. Audrey Penn's "The Kissing Hand" is great for this.
Remember, too, that although you are heartbroken when he falls apart, he needs you to be a good actor and pretend that you are confident he is going to have a good day and meet friends. A confident goodbye is so helpful. In my experience, the more we try to soothe, the more we try to reassure and reason, for some kids, this actually makes things worse. It's hard to say this and not come across as mean, but here goes: for some kids, our lingering and reassurance is very validating but in the wrong way. It validates the behavior. It tells them "you do have a reason to be upset". We don't want to be heartless, and we do want to work with the teachers. Now that the teacher knows your son is having a rough time of it, ask her to keep an eye out for him in the mornings. Try a quicker drop-off, keeping things upbeat and cheerful. If negative talk starts (or the sad predictions "no one likes me" "I'll be lonely"), I often answer kids with a matter-of-fact "well, now, you don't know that for sure. I saw lots of friendly kids here yesterday" sort of answer. Just stating the good facts.
It's tough, mama. If it continues to be tough after a few weeks, it's time to check in with the school counselor and ask for suggestions. Work with the teacher to develop a quick, positive drop-off routine. Our kids all have different challenges regarding school, and this is just one of them. Most parents won't say it, but many of our kids have their meltdowns on the way home from school, after they get home, or in the evening around bedtime..you just aren't seeing them. :) Also be sure he is getting enough sleep and a nutritious breakfast/a calm morning. Just my experience, but I found that kids who were experiencing a lot of transitions in the morning also had a harder time than kids who were well-rested and had a smoother morning. Consider no television before school, too. The reason for this being that watching tv causes the release of dopamine in the brain and when they stop, they actually go through a dopamine withdrawal. You want to eliminate any factors which could add to the emotions.
Good luck--hopefully things will improve for your son as you go forward. I know it's hard-- and it is SO hard to have the loud, crying kid, but you'll both make it through this. I promise!