Não informado. (1999). Shools in the middle. National Association of Secondary School Principals.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Shools in the Middle. Reston, Va: National Association of Secondary School Principals, 1999.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Shools in the Middle. National Association of Secondary School Principals, 1999.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.