My son's teacher might be a bully

I know my son, ***** can be a little toad sometimes. He's a boy...he's active..he finds it hard to sit still....but he hears everything, picks up on everything and is very bright. He gets bored easily.
A couple of weeks ago two women told me that they felt my son was being picked on by his teacher. These women do teacher help twice a week in my son's classroom. They noticed that ***** gets sent into 'time-out',' the thinking spot',' naughy spot' or whatever you want to call it very frequently (most days in fact) and for seemingly trivial things when other kids are getting up to much worse. He's been left out of practises for school productions and told he will be able to join back in when he can show he can behave. Other kids have been trying to stick up for him! He's only 5 - he's a lovely cuddly, kind wee boy - he has wonderful empathy for others.
Well...I didn't take too much notice. I gave the teacher the benefit of the doubt and some credit for having to deal with a lot, boys being boys etc. As I said I know ***** can be a little $%#* sometimes.

That was until today - today when I witnessed it for myself:

So....I was waiting outside the classroom in the sun - for the bell to go. I could see ***** but he didn't see me. He was sitting nice and quietly. Next thing I hear Mrs Teacher go off at him....."***** and Sajid if you don't sit properly we can't get this done before the bell goes (handing out books)". "***** sit properly". And then "Class, is this how we sit properly (no response from any of them)?" Poor ***** looked confused and went bright red, he didn't know what he was doing wrong or what he was expected to do. I moved over so that Mrs Teacher could see that I was there and gave her my hardest glare...he wasn't doing anything wrong! Others kids were standing, moving around, talking, laughing...not even sitting. How dare you make an example and embarrassment of my son! Fuckin' bitch. I don't trust her now and I hope to hell she doesn't change my precious boy into someone with no empathy.....

I am so upset and heartbroken.....I feel like my whole body has sunk into the ground. I've cried. I'm confused...I don't know what to do about it......AND.......

Another thing; a friend who has her son in the same class asked me "what I would do if ***** came home and told me that another kid had been touching his willy while on the mat?" Because that is exactly what her son came home and told her! What the hell is going on in that class?

Turns out that the boy suspected of inappropriate touching slaps my son often - but does he get sent to time out....no he doesn't.....he gets a final warning, then another and another......(so I'm told).