Society does not change on a dime, especially small-town society, said Deb Brown, a member of the Green Mountain Union High School board, speaking in MacLaomainn’s, a pub and popular gathering spot that she owns with her husband. For people like her daughter, who was on girls’ sports teams with A J when he was Autumn, this is intensely personal, not just philosophical.

“As we move forward as a community, there has to be compassion on both sides,” Ms. Brown said. “He needs to understand that this has been 15 years that students have known him one way. It’s obviously his choice, but maybe he should have respect for his classmates right now.”

Mr. Jackson has gradually been making the transition from a vivacious girl with a big smile and long wavy locks to a husky boy with chopped hair dyed several shades of green, snakebite piercings in his lips and gauges embedded in his earlobes. His chest is visibly bound, and because he has not yet started taking male hormones — he plans to do that, and also to have “top surgery,” he says — his face is smooth and still has feminine contours. He once thought he was lesbian, and is still attracted to girls.

His mother, Tracy, a case manager for children with developmental disabilities, and his father, Scott, a mechanical engineer, came to Vermont from Connecticut to try it out 20 years ago and stayed. They brought up A J and his older brother in a log cabin in the woods, where they raise chickens and ducks, including a duck named Bernie, for you know who.

“A typical American family,” his mother said, smiling.

He was in sixth grade when he realized he was meant to be a boy, he said, and came out to the school last year in ninth grade, sending emails to teachers. When he entered Green Mountain in seventh grade, “I was using the female bathroom because, I really don’t know, I was still kind of back and forth about my identity,” Mr. Jackson said. “This year is the year I started using the men’s bathroom, because I already felt like way more comfortable in who I was.”

There were practical issues. When he had his period, he wondered if he should revert to the girls’ bathroom, because there was no place to throw away his used tampons. But he had started feeling like an intruder in the girls’ bathroom, and the single bathrooms were so far out of the way it was hard to get to class on time.

So he stuck with the boys’ bathroom.

“I use a stall, and I wait till everybody’s gone to get up and leave,” Mr. Jackson said. “The guys, they look at me like I’m some kind of freak, or they’re concerned or scared.”