The chapter was good, however some of the the school things I have an issue with. I might be showing my ignorance, but the scene with the solicitor and Fredric Branck rubbed me the wrong way.
Having been the victim of that sort of thing myself, with a protected gang of boys, I can say that in America having an outsider show up like that and reveal herself would get her arrested for trespassing. They would be too busy calling the cops to listen to her evidence in the disciplinary matter.
Now at the station and in the courts it might be useful, but the attorney would still be facing the charges.
You should rewrite it so that Dudley has the tape recorder, and calls the solicitor and has her show up with his parents, THEN presents the tape recorder.
If Dudely were to show the tape recorder before that, it would be confiscated and the tape "accidentally" ruined before it can be used to prove his case. Not only that, but a new rule or an existing one would be put into play explicitly banning Dudley from having such a device for some made up reason like not being allowed to record the lectures or some other stupid thing.
That DID happen to me when I tried a dictation tape recorder with the micro cassettes. Approximately the same time frame as well. I did learn to give up trying to show my innocence however as well as any respect for the authority in question.
After that, they had the gall to wonder why I started being disrespectful to them and their authority in their "disciplinary" settings.
I also grew up as the favorite target of bullies. My father made it clear to all of us, that he wouldn't tolerate the social disgrace of his children fighting...regardless the cost. He went so far as to say to us: "I have enough kids. I can kill five of you and still have an heir."
In my case, the primary antagonist was a jerk named 'Biff' (no shit!) His dad and Coach Gentry were drinking buddies, and so he became the quarterback, and literally had the run of the school. He was a bully, an extortionist, and later, a rapist.
When my dad came after me for getting beat up, I told him that it was his won fault. After all, he'd told us he would beat us if we fought back. He beat me anyway, for daring to show him disrespect, as he put it.
Like you, I tried to get evidence (But back then, cassette recorders were huge, by today's standards) and like you, new rules were made up to prevent exactly that.
Fortunately my salvage came in the form of my elder sister who first taught me how to make various explosives and toxic gasses from what one could find in a normal household. From then on, I became expert in creating untraceable 'accidents'...usually explosive ones.
As for Carolyn, being solicitor for the Dursley family, she has every right to speak with her client,even on school grounds, just as long as she reports her presence to the office.
What happened was that she was on her way from the parking lot to check in with the office when she 'just happened' to come across the bullying students and their facilitator...in the act of attempting to extort money from a student.
Yup, that's her story and she's sticking to it!