In the United States, a middle school is a school between elementary school (grades 1-5, 1-7, 1-6, 1-4 or 1-8) and high school (grades 9-12 or 10-12). Depending on location, middle school contains grades 5-8, 6-8, 7-8, or 7-9. Middle school is also sometimes called an intermediate school, junior high school or just junior high.

The school day is often very different in elementary, middle, and high schools.  Unlike elementary schools, where students often stay with one or two teachers for most of the school day, middle school is usually the first time in which students change teachers after each class of usually about one hour.  Students often study 6 subjects. They will be taught by a different teacher for each subject.

The change from a one teacher-all subjects way of teaching helps create more independence for the pupil. They no longer have the guidance of just one main teacher.  Also, students will often have more of a choice in what classes they take. This is mainly in dealing with subjects which are taken in addition to the basic subjects such as mathematics, English, history and general science.

In general, middle school acts as a transition between the elementary school structure where most people are all treated the same and the high school structure were most people are treated as individuals. However, some critics see middle schools as having gone "soft," overemphasizing self-esteem building at the expense of academic rigor.

Historically, local public control (and private alternatives) have allowed for some variation in the organization of schools. Elementary school includes kindergarten through to sixth grade, or kindergarten through to fifth grade, i.e., up to age 12, but some elementary schools have four or eight grades, i.e., up to ages 10 or 14 (also known as the intermediate grades). Basic subjects are taught and pupils often remain in one or two classrooms throughout the school day, except for physical education, library, music, art, and computer classes. In 2001, there were about 3.6 million children in each grade in the United States. "Middle schools" and "junior high schools" are schools that span grades 5 or 6 to 8 and 7 to 8, respectively, but junior high schools spanning grades 7 to 9 are also common.

The range defined by either is often based on demographic factors, such as an increase or decrease in the relative numbers of younger or older students, with the aim of maintaining stable school populations. At this time, pupils are given more independence, moving to different classrooms for different subjects, which includes math, social studies, science, and language arts. Also, pupils are able to choose some of their class subjects (electives). Usually, starting in ninth or tenth grade, grades become part of a pupil's official transcript. In the U.S., children within this grade-range are sometimes referred to as "junior highers".

The “junior high school” concept was introduced in 1909, in Columbus, Ohio. Junior high schools were created for "bridging the gap between the elementary and the high school", an emphasis credited to Charles W. Eliot. In the late 19th century and early 20th century, most American elementary schools had grades 1 through 8, and this organization still exists, where some concepts of middle school organization have been adapted to the intermediate grades. As time passed, the junior high school concept increased quickly as new school districts proliferated, or systems modernized buildings and curricula. This expansion continued through the 1960s. Jon Wiles, author of Developing Successful K–8 Schools: A Principal's Guide, said that "[a] major problem" for the original model was "the inclusion of the ninth grade", because of the lack of instructional flexibility, due to the requirement of having to earn high school credits in the ninth grade and that "the fully adolescent ninth grader in junior high school did not seem to belong with the students experiencing the onset of puberty".

The new "middle school" model began to appear in the mid-1960s. Wiles said, "At first, it was difficult to determine the difference between a junior high school and a middle school, but as the middle school became established, the differences became more pronounced".

The faculty is organised into academic departments that operate more or less independently of one another.

The middle school format has now replaced the junior high format by a ratio of about ten to one in the United States, but at least two school districts had incorporated both systems in 2010.

Reference 

Types of educational institutions

de:Bildungssystem in den Vereinigten Staaten#Junior High School und Middle School
nl:Onderwijs in de Verenigde Staten#Middelbaar onderwijs