definition
strict definition
school
An educational institution for children or youths providing instruction below college or university level.
A school is any educational institution for children or youths, below the level of a college or university.
The pupils are children or youths, and the instruction is below higher education. A college or university does not become a school in this institutional role merely because it teaches students.
An institution restricted to supplementary adult education has a different scope. The presence of classes alone does not determine which educational role applies.