Please help me understand why my 5 year old has become aggressive

[WomanEmpire]

5 incidents within 8 days of school. Up until Christmas he loved school and had no behaviour issues. He's been in nursery since 8 months, and has never struggled socially with children or adults.
His teacher went on Mat leave and I know he found it hard, there was a small incident which knocked his confidence a few weeks ago, no point going into it it's been handled but he was upset by a member of staff.
I've been called in twice, sat and created a behaviour plan with them and I'm sick with worry. There are 3 incidents of scratching, the other 2 are play fighting (about 4 or 5 of them get disciplined for this)
All of the scratches have happened after being provoked, not out of the blue, but pretty nasty.

We can't see any issues with bullying and the behaviour isn't continuing at home. He can sometimes be rude, but he is disciplined for this (step and/or loss of screen time) he knows he is supposed to find his teacher when he's either getting angry, or he's been hurt, but he's not doing it.
I cried today in the playground as the teacher spoke to me (for the 2nd time that day) as I'm just at my wits end. I want to understand why he is doing this, so I can help him.

Would reward charts help? If he got a star for every good day - working towards a little treat once he builds up a managable amount like 3 or 5 good days. Lots of praise for the good days. Reminders before he goes into school about trying his best.

Encourage him to use his 'ignore muscle' on people he feels are provoking him.

Make sure the teachers on yard duty will allow him to tell if something happens as an alternative to lashing out. Sometimes teachers are bombarded with children telling tales and may be a bit dismissive which could be frustrating for him.

My son went through a phase like this and I felt awful - he's 8 now and has been well behaved in the yard since that episode when he was 5.

He’s still learning, OP. He is only 5, so he still has poor impulse control and acts on the spur of the moment rather than weighing up the long term outcomes (I’m referring to your comment “he knows he is supposed to...”) - this is just the developmental stage he’s at. I’m not saying you shouldn’t deal with this firmly, of course he must know that it’s not acceptable to hurt other children, but I think it helps to remember that this sort of thing is normal at this age.

Reward charts may not help because it's his behaviour at home, not school. He has that kind of system at school now and gets very upset when he doesn't get the free time, but it doesn't seem to be improving the behaviour!

He is still young, I know, but I worry this will impact not only education but his overall enjoyment

Ignore muscle is a really good idea

Maybe you could role-play with him at home. You take the part of a child who might be provoking him a bit - and he can practise ignoring the behaviour or trying to tell a teacher if the ignoring isn't working.

I always told my son he will end up looking like the bad guy if he hits and people won't notice what the other person firstly did as all they will see is the hitting.

Sorry I'm the update I meant the behaviour at school is the issue, not home.

The role play is something we have tried. He had a good day today so hopefully this continues. It's one child in particular that he tends to always be in an argument with, who is always his best friend. Unfortunately they can't be split up as there is only one very small class

My child went through something very similar at school at around 4.5. It lasted about two months and then was gone never to return.

We did social stories - you can find them online and actually write your own using the app book creator with real photos of him in.

We did role play with teddies showing them making the wrong and the right choices.

We did lots of praise for good behaviour.

And also which was very effective read a book about feelings and talked about recognising mixed up feelings. The colour monster book is very good for this.

School did discipline firmly for the bad behaviour which was right, but also worked on his self esteem - he was singled out for a classroom job and given public praise in front of the other kids for one thing he is good at (he was very behind on writing etc then)

I’m sure you’ve thought of lots of this!