Hard disagree that Andover is “cutthroat” as someone mentioned above. The kids are for sure intensely driven (sometimes to unhealthy levels) but not in a way manifested by sharp elbows, at all. They compete with themselves, but are always helpful with others.
I’ve observed this firsthand with my 2 kids (day students, so I literally do see it first hand when they help others…tutoring, homework help, group projects, etc).
Elitist? Sure, that I will cop to.
As for sink or swim, yes - the resources are there for all the help you want or need, but you have to seek them out. No one will force you into the academic skills center, to conference (aka office hours), mental health services, etc. So in that regard it really does function like a college. Now, there will of course be strong suggestions from your advisor, teachers, etc. But if you don’t pursue those resources, that’s basically that. Sink or swim.