son displaying different behaviour in school than home...advice needed

hi my soN sure waiting for diagnosis shows different behaviours at home than in school, in school he is quiet and at home he Is having meltdown hitting spitting throwing things etc the best way I can describe him is like he is a bottle of coke in school he is quiet getting shook up all day then when he's at home around people he feels comfortable with he is exploding. Now the battle isn't with my son I'm doing everything  can to help him until he gets a diagnosis but it's with the school, it's like they are blind and don't understand things for example today I picked him up and he came out, looking upset when I asked what's wrong he said his friends so when I asked his teachers they just kept saying oh no he's been fine, he's good as gold, he never tells us anything and this is what kids are like. It's like they are patronising me and don't believe a word I am saying, when I knew what would be coming when I get home. They then started to ask my son, what had happened and putting words in his mouth, I had to walk away and said I'm sure I will find out when I get home and they said well yeah tell us when you do.

Now my so. has come home bit, smacked  my daughter, threw loads of toys about, smacked me pulled my hair bit me and is just had a full on meltdown, all because of what's happened in school. He's only calmed down from 10 past 3 at about half past 4, I feel like the school are just patronising me and making me feel like I'm a soft mum and can't handle him ( I work with children, I have twins, my son and then my daughter I'm well aware of how to handle children) the school are aware we are waiting on assessment from Camhs and I have been told to document everything thats why I asked them what had happened today.

i just feel like because he is showing different behaviours that the teachers don't believe a word I say and look there nose down at me. I was just wondering has anyone been through this or does anyone child display different behaviours in school than at home and how did they get on with school, because I'm finding it really difficult in getting school on my side.

thankyou for any advice x