[aidenn0]

They are all assigned by address; so there are N elementary schools that feed into a single junior high (or middle school), and typically a junior high will feed into a single high school. So your friends move up with you unless someone moves.

This is all "typical"; there are many exceptions. Where I live now, they unified the secondary schools (i.e. junior-high and high-school) so that you can apply to go to a different junior-high or high-school than your local one, space permitting. Similarly where I grew up, you could apply to go to a different school, but a "legitimate academic reason" was required. People did game the system, most commonly by claiming they wanted to study a foreign language that was offered at the school they wanted to go to, but not the school they were in the district for.

I should note that where I grew up the school-system was unusually non-local in the sense that there was one system for the entire county (which was about half the land area of Saarland). Even then you were required to go to the local school though. More typical is that each town or city manages the schools for their area.