A selective school is a school that admits students on the basis of some sort of selection criteria, usually academic. The term may have different connotations in different systems. The opposite is a comprehensive school, which accepts all students, regardless of aptitude. The split between selective and comprehensive education is mainly seen at secondary level; primary education is rarely selective. At the university level, selection is almost universal, though some institutions practice open admissions or open-door enrollment allowing students to attend regardless of prior qualification.