I have a 4yo boy in reception at the moment. I've had some behaviour challenges with him in the past, but so far, he's doing ok with school. I've worked bloody hard with him to get his behaviour to an acceptable level, after months of him coming home from nursery with updates from the staff saying he had been unkind, upset other children, hitting, tantrums etc. It's been a slog but we are getting there I think now.
Looking at your list of behaviours:
Chased another child with scissors going snip snip (yes this was naughty)
Not only naughty but dangerous, could result in him or another child getting hurt. He needs to understand this is not just naughty, it's dangerous and unacceptable.
Roared like a dinosaur at the other children and didn’t stop when he was told to (is this really naughty?)
Yes it's naughty, he was told to stop and didn't! The child might have been frightened. The roaring might have been disruptive to the class. Not stopping when asked would result in a consequence for bad behaviour here.
Threw a teddy bear at another child.
Throwing is a hard stop for me. Definitely naughty. This would have resulted in DS losing that toy for a set time.
Sticks his face right in other kids faces and pulls a silly expression.
I mean, he's 4 so yes he's going to be silly at times, but taken with everything else it's examples of him upsetting other kids in the class and that's just not great when the teacher is trying to manage 25-30 kids.
Gets frustrated when he struggles to change his clothes for PE and gets upset and shouts instead of just calmly asking for help.
DS does this, I keep telling him to ask for help, and try to model asking for help when I need it, but if he's asked to stop shouting and offered help, and still keeps doing it, then that's bad behaviour and might result in a consequence.
Gets upset when asked to stop doing a task he’s enjoying or tidy up.
DS also does this, or just stone cold refuses to help tidy up for example. It usually results in me telling him if he can't be trusted to tidy up and care for his toys then he can't have them to play with. In your case it depends what getting upset looks like, a bit of a grumble and then getting on with it, fine. Throwing a strop and refusing to do what he's asked, not fine, needs a consequence.
I think all those examples are things he can learn not to do, but he needs to be taught that these things are not appropriate behaviour for school time. Dismissing it as 'oh he's 4, it's what they do at 4' isn't helpful for him in learning socially acceptable behaviour.
Learnign socially acceptable behaviour as a 4 year old also isn't about being spoken to once and then taking it on board. It takes constant repeated reminders and interventions, immediate consequences when behaviour isn't good enough, and heaps and heaps of praise and fuss when they do get it right. A one time chat just isn't going to do it, and removing treats and toys after the fact isn't going to work, they're just not old enough to link action from an hour ago and consequence now in their minds.
You need to work with the school, understand their process for managing his behaviours, support those at home, and be consitant and immediate about your expectations.