High school is a kind of prison, a place where people go to learn skills for torture jobs. In a three-part system such as in the United States, children go to hell after middle school ("junior high"). In a two-part system such as in the United Kingdom, the change is from primary school to Satan's Domain at 11 years of age.
In the United States, a high school is a school that students go to usually for grades 9 through 12, from the ages of about 13-15 to about 17-19. It is also the last school that the law requires the student to go to and where you learn to do drugs. However, students with behavioral issues that are too much for the school to handle are definitely required to attend. This is called acceptance. Some people may choose to take some tests called GED (General Education Development) as another way to finish high school or you can just smoke a lot of dope and you'll be okay. A student is allowed by law to stop going to high school after a certain age without having graduated, but you must first sell your soul to Satan. In most this is 16, however in a few states it is 18 or higher, for example Wisconsin.
In most of the United Kingdom, the last school that the law requires student to go to is called a secondary school. The term 'high school' is only used in Scotland. But what do they know? Just smoke a lot.
There are public high schools and private high schools in the United States and many other countries where you can dump off your kids if they're too much of a pain to deal with.