A secondary school is one means of delivering education to adolescents in level 2 or junior secondary education, which is considered the second and final phase of basic education, or level 3 (Upper) secondary education phases on the ISCED scale. Every country aims to provide schools for basic education, but the systems and terminology remain unique to them. Secondary schools typically follow on from primary schools Attendance is compulsory in most countries for students between the ages 11 and 16.

In the United States, the term ‘secondary school’ can refer to several types of schools. The first type is a traditional, comprehensive high school, comprising grades 9–12. Another type is alternative schools, including continuation schools, which serve those same grades. In some jurisdictions, ‘secondary school’ may refer to an institution that houses grades 7–12. The term ‘secondary school’ also categorically includes both middle school and high school. This page lists many secondary schools in the United States.

Students at Think Global School engage in place-based learning activities around the world
As a practical matter, while laws in most states mandate school attendance at least until age 16, many require attendance until age 17 or 18 (unless the student earns a diploma earlier, usually around age 16). State laws vary on the cut-off age for students to receive free public education services. Students can stay in high school past the age of 18 up to the maximum age limit to which free education must be offered in their state. Many states also have adult high schools for people around 18 and over. According to the National Center for Education Statistics [18] 81 percent of students graduated high school on time (within four years after having entered high school as freshmen) between 2012 and 2013. A high school diploma or General Educational Development (GED) certificate is usually required for entrance into a two or four-year college or university and to other post-secondary education programs.

High schools can usually be sub-classed as general high schools, vocational schools (VoTech schools), magnet schools, and college preparatory high schools (prep schools) and special high schools or alternative high schools. Most high schools are general high schools. These general population schools offer college preparatory classes for advanced students, general education classes for average students, and remedial courses for those who are struggling.