A head teacher, headmaster, headmistress, head, chancellor, principal or school director (sometimes another title is used) is the staff member of a school with the greatest responsibility^[1] for the management of the school.

In the past, the headmaster or headmistress of a British public school was often the owner of the school or a member of the owning family, and the position often remained in the family for many generations.

In Scotland, the holder of this position is sometimes known as the "rector"; however, usage of this term mainly applies to independent schools. The slang term "heidie" is seldom used in Scotland today, and most Scottish schoolchildren now refer to their head teacher as "the head". In North America, Australia, New Zealand, Hong Kong and Ireland (including Northern Ireland), the position holder is usually known as the "school principal", but some schools, primarily independent schools (called "private schools" in North America), use the term "headmaster" or "head master". As in Scotland, the term "rector" is still in use in the United States in private religious schools, as by tradition the head of school was also a priest. Some American state schools (called "public schools"), such as Boston Latin School, Brooklyn Latin School, and Milpitas High School, also use the term "headmaster", either because of the schools' history or historical connections.

In the UK, the terms "headmaster" and "headmistress" used to be the formal titles in most state schools as well as private schools, with "head teacher" only being used as a term to refer to them collectively.

In recent years, however, most state schools have switched to the gender-neutral "head teacher" as the official title.

Nevertheless, the gender-specific terms are still commonly used in day-to-day speech and are still the official titles at some of the remaining state grammar schools and most private schools. Some use other terms, such as "high master". In South Africa, independent schools and the majority of state schools use the gender-specific terms "headmaster" and "headmistress" when addressing their head teachers.

"Principal" or "head of school" is often used as the title of the head administrator of an elementary school, middle school, or high school or boarding school in some English-speaking countries, including the United States, India, Australia and New Zealand. Public schools in the United States generally use the title "principal" whereas private schools in the United States sometimes use the title head of school.

While some head teachers still do some teaching themselves, in most larger schools, most of their duties are managerial and pastoral. They are often used to discipline misbehaving students, help organize school sponsored activities, and all teachers in a school report to the head teacher.

In Australia, the head teacher is sometimes in charge of one (in the case of a major subject) or multiple (often in smaller schools) specific departments, such as English, history, maths, science, writing, technology, etc., but maintains full teaching duties and status.

They are considered part of the school executive, and often a head teacher position is a stepping-stone into administration.

In larger schools, the principal is assisted by one or more "vice-principals", "assistant principals", "associate principals", or "deputy principals". Their position is secondary to the principal with regard to school governance. Assistant principals generally perform specific duties such as handling student discipline, curriculum, student council or student activities whereas the principal has the ultimate responsibility for the school as a whole (including faculty and staff, physical plant, etc.).

In many Australian and New Zealand schools, a headmaster/principal is the head administrator of a school who has been appointed to her/his position by the school board, superintendent, or other body. The principal, often in conjunction with the school board, makes the executive decisions that govern the school, as well as having the authority over the employment (and in some cases firing) of teachers. The principal is often the chief disciplinarian of the students.

In 1999, there were about 133,000 principals and assistant principals in the United States.^[2] In the early decades of public education, the full title was "principal teacher", which accounts for the present day title having an adjectival form, essentially being a shortened version of the original full title.

Yet the terms headmaster and head of school are still used in some older schools.

School principals in the United States are expected to have school administrator licensure, and, often, a master's degree in educational administration.^[3][4]

While there has been considerable anecdotal discussion about the importance of school principals, there has been very little systematic research into their impact on student outcomes.

Recent analysis in the United States has examined how the gains in student achievement at a school change after the principal changes.

This outcome-based approach to measuring effectiveness of principals is very similar to the value-added modeling that has been applied to the evaluation of teachers. Such research in the state of Texas found that principals have a very large impact on student achievement.^[5] Effective school principals have been shown to significantly improve the performance of all students at the school, at least in part through their impacts on selection and retention of good teachers. Ineffective principals have a similarly large negative effect on school performance, suggesting that issues of evaluation are as important for school administrators as they are for teachers. The impact of principals has also been measured in non-traditional ways. Some principals have focused their efforts on creating more inclusive schools for students with disabilities.^[6]