In England, they tend not to owing to a shortage of beds and a belief that this is the kind of problem that is best managed in the home environment.
I believe in the US, it's different. From what I've heard (and depending on your insurance) even uttering the word 'suicide' can lead to hospitalisation. In the long term, it'll be better for you if you tell your school therapist what's going on; at least then they'll hear it from your mouth, instead of a distorted version from your friends.
Psych wards aren't as bad as they're made out to be. They exist to allow the psychiatric profession to carry out intense observation and treatment, to help you recover as quickly as possible from bouts of psychiatric illness. They're not prisons, and they don't tend to keep you for longer than necessary. if they want to send you to one, they will discuss it with you, and you'll have some input. So try not to worry, they just want to help.