Agree with @AnonMomof2 . Our kiddo’s experience at school has been that students are respectful of each other and more embracing of a each other as individuals compared to kids back home at the local school. There is an emphasis on acceptance, respect, & community building. Not just for students who are LGBTQ, but for everyone. IMO, most BS’s self select for intelligent students who can (or willing to) live away from home in a community.
It works both ways. Are there kids who don’t desire, feel comfortable, or seek to be part of a greater community? Sure. For that student, there is a choice of schools and they should look for a school that fits their needs/desires.
There are differences in boarding schools @ their emphasis on and in the ways they build their community in totality, versus indentity-specific community building. So, might be helpful to examine what you and/or your student value, desire, expect and need from a boarding school.
There are some boarding schools, for example, that offer specific dorms for students who might be transitioning. Also, there are some schools that offer unique living options for uppers with common lifestyle needs or desires.