If it was consensual, give him 5 years and make sure he never works as any kind of authority figure over children, teens, or even adults ever again.
My ex (maybe back again, who knows) is from Montenegro.. There, all the parents apparently wanted the male teachers to have sex with their 15-16 year old daughters, because they were educated, had good jobs, were respected in the community, and they would usually get married. Her brother knocked up a girl right before she turned 15, he was 22, they got married and it was not problem. They moved hear (New York City) when she was 17 with 2 kids, they are still happily married 12 years later. That's how people meet and get married there. That's Montenegro.
Here, we expect and demand 14-26 be filled with soul crushing immoral sex with multiple (dozens, really) of partners for women, including at least some lesbian sex for girls. Usually a couple threesomes, and probably some recorded porno sex. THEN a man can settle for that women, with the women never respecting him because those 14 guys she had that one year had bigger dongs and treated her more like a whore, which she probably thought was real cool.. That's America.
In America, it's not normal to get married very young.. That changes things. I'm not saying either is better, btw, and as a 37 year old of modest means, I think 25 is about as young as I would feel good about going now..
Around the world, I don't think you get groups of lonely internet white knights pretending to be outraged at sex 95% of them would have if they knew they wouldn't get caught. In America, I honestly would NEVER have nailed a 15 year old as a 26 year old teacher; that's not cool here, and I'm not saying it is. But I'm not going to indulge any male instinct and pretend I'm outraged by other males having sex, like it means more for me lol. Just make sure this guy never teaches again, and give him a high five years in prison for a lack of control.
He won't get a molesters treatment in prison if it was consensual, because she wasn't a child and the guy didn't prove he was a pedophile. He's an idiot with no self control in the wrong business.