@Stressey I could have written your post and I am a teacher! I have taught in secondary schools and now work in primary and my daughter in Year 9 is displaying similar behaviour to yours. I’d like to think in this day and age that nobody would judge you as parenting teenagers is hard!
My eldest daughter (year 11) is at a different grammar school, works hard, is polite and is doing really well. I don’t think that makes it any easier for my younger one and she can display low level disruptive behaviour in school. Any teacher knows Year 8 & 9 is a difficult time due to hormones and often a time when friendship groups etc can change.
Some of the things we think are affecting my daughter and could be causing her behaviour are: friendship issues, she has had a difficult time with friendships; low self esteem, not thinking she’s good enough, as obviously she is at school with a lot of academically bright children.
Some of the things we are doing to try and help her and to address the behaviour are: an open and honest dialogue with her head of year, I found it really helpful going into school to try and see if both us as parents and her teachers can try to help her manage some of the emotions behind her behaviour; identifying people she can talk to at school and at home when she feels overwhelmed or frustrated, which seem to be the emotions behind her negative behaviour; just being there and knowing she can talk to you - checking in regularly and just letting her talk if she wants to, but also not forcing her if she doesn’t.
We found taking her phone was not helpful at all. It meant she felt isolated and lonely as teenagers now communicate differently with each other, always through the phone, so this only added to her anger and frustration and negative behaviour. I do though talk to her about her phone (and check it with her consent if I feel I need to), ask her what she is doing and whether she is receiving (or sending) unpleasant messages as if I thought bullying through the phone was adding to her behaviour, I would think again.
I hope some of this is helpful. Good luck xx