Hi I know your question has been answered about twice already, but i thought i'd add my little bit, because of the way my school is.
Originally Posted by kehribar
You don't always have middle and high schools, there are different systems for different areas of the country. In some areas they have something called the Three Tier System where they have Lower School (ages 4-9), middle school (10-13/14) and Upper School (14-a maximum of 18). In other areas (i'm not sure about the ages because i have never been to one of these) they have the Two-Tier System where they combine Middle and Upper School and Middle and Lower. Confusing But some schools are known for being really good, and lots of parents want their children to go there. Most of the time you go to the school in your catchment area (the nearest school to you), but if your catchment school isn't as good as another school then you can apply to go there. You can't alwasy get in though. Every school must let in everyone in the catchment area, but if they have any room left they let in the first-chosen. If you're not one of the first chosen, you have to go to your catchment school.
With some Private schools (in case you didn't know, Private schools are just where you have to pay to go there) you have to take an exam to get in. If you don't get a certain mark on the exam then you don't get into the school. This is so that only people on a certain intelligence get in the schools.
So, to answer your question, for some schools you have to be at a certain standard, and for some schools it's just first-come first-serve.