In the United States, children start school when they are five years old. In some states they must stay in school until they are sixteen. Most students are seventeen or eighteen years old when they leave secondary schools. There are two kinds of schools in the United States ------public (公立的)schools and private(私立的) schools. Most children go to public schools. Their parents do not have to pay for their education because the schools receive money from the government. If a child goes to a private school, his parents have to pay enough money for his schoolings. Some parents still prefer private schools, though they are much more expensive.Today about half of the high school students go on to universities(大学)after they finish the secondary schools. A student in a state university does not have to pay very much if his parents live in that state. Many students w---- while they are studying in universities. In this way they develop (发展)good working habits(习惯) and live by their own hands.