We are also working on this issue as we put together a plan for my 6 year old DD. For her the meltdowns tend to come when adults don't give her a chance to explain herself. She really can't handle being accused of things that she didn't do. Part of it is that most people don't expect such a little kid to have the vocabulary and verbal skills that she has. This means that even if she tries to express herself adults tend to be thrown by the words she is using and don't pay attention to what she is telling them. I am asking her new school - and have had it included in her IEP - to assure that she has the opportunity to be heard.
The other thing we are hoping will work is a request that if she gets upset the school call me, at least until she has established a rapport with a safe adult there. I assured them that I will not pull her out of school, thereby rewarding her behavior. I just give her the opportunity to tell me what happened and that is usually all it takes to calm her down. I made sure the school knows she doesn't get her way just because she is upset - the answer is very often "no" or an explanation that she was wrong. That is ok with her as long as she knows that she had a chance to be heard.
From the time she was a baby (maybe 18 months old) she would put herself into time out when she got upset - after calming down she would come out and try to explain what was bothering her. If she was not allowed to remove herself like this she got more and more upset until she hit full blown meltdown. Now that the anxiety from kindergarten has abated over the summer we see she is doing this again - first time we realized she had stopped while in her awful school situation last year. The IEP allows for her to remove herself from her classroom to take a walk or get a drink if needed. I think it will really help.
Not sure if this is your child's issue but thought I would throw it out there. Good luck figuring it all out!
