Or, you're a female member of staff. You have a youth who is significantly taller than you and has developed a lot of muscle bulk over the last year. He has already pestered you to add him on Snapchat (knowing that the main appeal of the thing is being able to send images and their then being deleted after a set time) and, despite trying to explain how uncomfortable this behaviour is, the youth convinces his Mum and everybody else that it was 'just a joke'. He's still in your class.
How do you discipline him for such things as no homework? That would mean having him alone in your room after school, which you aren't comfortable with. It's not an offence that warrants a senior team detention, the rules are that it's a teacher/short detention. Hopefully, somebody else fails to hand their homework in at the same time. Or you don't do anything for fear of a) laughing and saying you just want to get him on his own = you are a paedophile b) laughing and saying he can't wait to be alone in a room with you and c) him complaining to his Mum that she's picking on him. You can feel that you haven't got as much authority as a teacher and your skin crawl in the same way it does when a bloke in a pub comes up and tries to get you to give him your number.
It's winter, so it's dark. Most school sites are poorly lit. Is it that creepy kid that sets off your alarm bells over there? You ignore it and try to pretend everything is OK. He's a kid. Just a kid. Don't think about he way he sizes you up and down with his eyes like a fully grown predatory man might. Don't think about it. Pretend it's not happening. Ignore your instincts to escape.
And then the youth gets way too close to you and exposes his body. If he's like most teenagers, his trousers are barely hanging onto his backside at present, so you get a sight of everything to just a short distance above his pubis. You can see whether he has pubic hair that extends above that. He's demanding that you look at him. Other kids are laughing. You can't walk out of class. You've got to request on call assistance and those five minutes are the longest imaginable.
Yes, this isn't necessarily exactly what happened, but the feeling of having somebody be so creepy is just as traumatic when they're 15 as when they're 45 - even more so when you take into account that you could be blamed or accused of leading them on and your career ruined if he takes rejection badly or another youth gossips to their Mum about how their teacher fancies x.
He's been excluded so that she feels safe in her working environment. It's not to inconvenience you or annoy him - it's for her safety. Teachers have been assaulted before. He has deliberately made her feel unsafe by acting in a disrespectful, predatory & overtly sexual way towards her.
The best thing you could do for her feelings of safety is to ask for a managed move. If he stays at the school, even in a different class, he's still there. He could still be around when she's alone in the classroom marking or updating a display at 5pm, there aren't many staff within shouting distance or when she's leaving.
But I'm sure you won't do that - after all, why should he have his exam results potentially damaged for a few minutes of sexual harassment?
I see that you appreciate he has done something wrong, but I don't think you appreciate how much he appears to have scared the teacher concerned - or how sensible the school is in acting upon this immediately.
He needs to not have X Box, phone or internet access (or the gym - he's not supposed to be using weights until he's 16 anyway, according to most gyms). I'm willing to bet that he spends a lot of time accessing pornography that is violent in nature, too.
I hope your OH understands just how bad this is and makes it abundantly clear to him that this is not how you act towards ANY female.