My DS is 5, in year 1.
He doesn’t tell me much about school, we had a recent parents’ evening where I was told he is very capable, reading doing well, and things to work on were not shouting out/waiting his turn to speak. His teacher told me he and his two best friends (one whom is, I hate to say it, the “naughty” boy in the class) have to be separated in the class as otherwise they get too overexcited. She also said that DS almost “heckles” her sometimes (she didn’t use that word, but I can’t for the life of me recall how she said it).
I was relatively happy with how this parents’ evening went as there weren’t any surprises - since he’s been in Y1 I’ve never been spoken to about his behaviour, and I wasn’t in reception either, but in the summer parents’ evening in YR I was told he’d started shouting out/silly noises during quiet time. This came as a surprise to me at the time as I had never been told about it.
This week I found out from DS that there is a reward system in place in class, a cloud, a tree, a sun and a rainbow. Everyone starts on the tree, and if you’re naughty you get moved to the cloud for the rest of the day. If you’re good, the sun, and if you’re “star of the week” you go to the rainbow. At the time DS told me he’s NEVER been on the cloud, but that his “naughty” friend goes on there all the time. This made me really sad for his friend at the time, who isnt a bad child at all, but he is very emotional/over the top and so I can imagine for a teacher with 30 other children, he can be disruptive.
Today DS confessed that actually he has been on the cloud, 4 times according to him. I asked why, and he said for whistling while the teacher is talking 
I asked him to show me how he whistles; it’s basically just calling out loudly. So disruptive behaviour essentially. He said he has also been on the sun too, a few times, but that only he and his “naughty” friend have been on the cloud.
As mentioned I’ve never been spoken to about his behaviour by the teacher other than the parents’ evening. My DH thinks I’m mad to be worried about this, but I hate the thought of only my DS and his friend going on the cloud, as it singles them out as the “naughty” ones. I thought about trying to ask his teacher for more information about this system, and how we can support school with DS’ behaviour (eg if he has been on the cloud I would like to know so he doesn’t get screen time that day, similarly if he is on the sun I can praise and reward him) but to be honest it’s almost impossible to speak to the teacher privately unless I call the office and ask to pass a message on to call me back.
WWYD? DH thinks I’m massively overreacting and if his behaviour was a big problem, we’d be spoken to after school.