Three year old not listening at school

I have a 3.5 yo son. He goes to a montessori school, with a class of 12 others. He was doing really well there (minus the first two weeks where he was still adjusting to the new classroom) but I had my mum come up and visit me for two weeks, she's a shitty mum and I had hopes she would be a better grandparent but it was not the case, while she was here she said mean things to him, would threaten to leave when he would get upset (like a three year old does) and I made the mistake of letting her put him to bed, where she would feed into his desires and what was a good easy 7 o'clock bedtime turned into 10.30 after hours of screaming.the first night i put him to bed again after I realised this wasnt going to get any better, he went straight to bed without any fuss, then he tried to call out to his grandma. She responded, he called out again, she responded, he called out again, she ignored him and he got upset. Not a tantrum, he didn't do anything but cry at the door. I asked her not to respond to him because it'll only encourage him to do the wrong thing and she just snapped and lost her shit. SHe dragged out her suitcase and started screaming at me and him that she had had enough and couldn't take this anymore. I tried, desperately, to make her see reason but after 40mins of her trying to make herself to as the victim, bringing up all sorts of things I lost it and demanded she leave.My son heard the whole thing. I tried to say that grandma had to go because she was sick, but he started saying things to me like "When i grow up and have a baby, and he wont go to bed, im going to get my suitcase and leave.' I tried to tell him that grandma did the wrong thing but I seriously underestimated how much he mentally was holding from the eventsince then his been an absolutely terror at school, never listening to his teacher, throwing others kids toys through the fence, getting scissors and cutting up other kids work. The other kids in the class have turned against him, none of them say goodbye to him anymore and they all say to their parents 'that boy doesnt listen in class.' and its clear the teacher is trying but fed up with it.I'm so hurt and at a loss of what to do, he was doing so well and was so happy to go to school and now he begs me not to go and he looks so cut up when he sees the other kids at school. I tried talking to him more about it, we had a good hour long chat about it tuesday night where he told me a lot more about what he had heard and how he thinks me and his teachers will get our suitcases and leave him.On wednesday i kept him home from school and when he had a tantrum I kept saying to him 'its ok, I still love you and i'm not going to leave you' and he'd hit me and scream at me, which he doesn't do much, and i kept saying to him 'I don't like it when you hit me, it hurts, but i still love you and i'm not going to leave you' to show him that his fears aren't true.after that his been much much better at home but today, Thursday, he still acting up at school. I really cant describe how upset I am for him, that i didnt protect him from my mum's bizarre behavior and how its affecting his likeability at school. The teacher's trying to work with me, but by the sounds of it she doesn't have any experience dealing with badly behaving kids as she has always been at pleasant montessori schools. What can I do to help him when his at school? How do I unfuck this? via /r/Parenting https://ift.tt/2FHKdlD