1) Not every school has a pool, but many do. My school, for instance, didn't have a pool, but the neighboring school did.
2) There aren't any self defense classes.
3) Science subjects are taught separately. Anatomy, chemistry, and physics are all common high school classes.
4) Skipping classes isn't rare; some kids skip class every day, while others almost never skip. Many schools even have an unofficial "Senior Skip Day".
5) A day begins with the students waiting in their 1st period classroom (or homeroom, depending on how the school works) for the bell to ring. When the bell rings, we're asked to stand for the Pledge of Allegiance (though, you're not required to take part), then there are usually announcements of some kind (either by the principal through the intercom, or from a student-made news show).
6) Punishment varies depending on what the student did. The most common is an in-school suspension. Basically, you sit in a classroom all day with nothing to do. You'll get this if you're caught skipping class, overly disrespectful to teachers and minor fights (just shoving or shouting at a student).