Not saying it's easy, especially for a kid, but if you go in front of a panel like that, if you can demonstrate remorse and desire to change, it goes a long way.
It sounds like you're presuming to know more about what happened there than you can. I fully expressed remorse, and explained how in hindsight I understand that what I was doing was disruptive, and that I wouldn't behave that way in the future, etc.
Their rubbish analysis was just that. Also, how is "slouching" a fair thing to observe in analysis? I sit with bad posture. I did then and I do now. It's completely irrelevant.
Oh, I should also point out that by this point I had been clinically diagnosed with ADD - which they expressed, and I'll have to paraphrase as it was about 13-14 years ago, was "made up" and that it couldn't possibly explain my behaviour.
This only furthers the advantage of those most willing and able to lie. Especially so when the system and punishment is arbitrary and capricious rather than rooted in first principles. We should focus on outcomes and shared goals, not easily faked attitudes.
The presence of the word "only" clearly makes an assumption that it is a lie.