My son is in Kindergarten.
It takes... TIME to adjust to Kinder.
Kinder is more structured and there are lots more expectations.... and a curriculum.
And kids.... are tired already, or get tired, and hungry and over-stimulated too.
All of that, affects a kid.
Normal stuff.
Not only with your son.
Going to Kinder, everyday now, and all day... is hard "work" for a young child. They get, by the end of the day... just OVER tired. And need a nap when they come home, if you can get him to nap.
If like my son, my son actually gets more HYPER and boisterous when he is tired. AND he will actually tell me he is tired and wants to nap.
On days my son does not wake up well in the morning or is tired, I tell his Teacher. Just as a head's up. She always appreciates that. It does not happen often... but I just let her know.
Because most of your son's issues, occurs in the afternoon.... I would assume he is just TIRED, already, by then.
AND if he did not eat lunch, or if he did not have a good lunch... well an empty stomach... would make any kid or adult... just NOT themselves, by afternoon. That is a LONG time to go, on an empty stomach, since breakfast time until the end of the school day.
Low-blood sugar, really affects a kid's attention spans/moods/behavior.
I volunteer at my kid's school. MANY kids, do not eat lunch. Because... they don't like what is served or they don't like their home-lunch. Thus they do not eat... even if, hungry. So then that means, their empty stomach, WILL affect them... in school, later, and by afternoon.
I see that all the time, kids not eating lunch or barely.
Then by the end of the day, they have nil patience or ability, to stay on task and concentrate.
So, just a thought. Because, that is a factor too.
My son's Teacher says, it can take at least a couple of months, for a kid to adjust to it all.
It is a whole lifestyle change, for the child. Even if they went to Preschool, prior. Kinder, is very different.
And besides, NO kid, is still as a statue.
The Teacher, should know that.