Kids at that age do not understand the difference between a need and a want. Being able to run to the toilet without permission because there was a toilet emergency would be categorized as a need. Wanting to go home in K because the child is not feeling good (tummy hurt, sleepy etc) is a need, in my opinion.
Things like wanting everyone to be absolutely quiet at circle time (my son used to be very annoyed at all the chattering kids and start trying to mange the crowd himself), needing to stretch, wanting a drink of water can usually wait - circle time is usually 15 minutes in his school and we even taught him to watch the clock so that he would not feel like he was waiting for an eternity (it feels like that to 5 year olds) and feel helpless.
I would encourage him to wait if there was no emergency. Recess and snack time are usually a good time to go to eat, drink water or to make a bathroom trip.
In order to support the teacher, you can tell him that the teacher has some class room rules and they have to be followed in order for all involved to accomplish what they have set out to do. Emphasis on how rules are made for the general wellbeing of everyone would make him think on the lines of co-operating rather than questioning the rules. Also assure him that rules are not rigid and that they evolve and the teachers can and will review them as needed
The teachers and rules are there to ensure the welfare of all the kids and knowing that will give him a different perspective.
Also tell him that it is OK to take his feelings of being wronged to the teacher and discuss them with her - because she would not understand that he felt that way unless he talked to her. This also teaches him that in a democratic setting he can speak up when he feels wronged and he has freedom of speech, but he also needs to wait for the appropriate time (after circle time) to be heard.
