APA

National Education Association of the United States. Dept. of Elementary School Principals, . (1948). The principal and audio-visual education. Washington: .

Chicago

National Education Association of the United States. Dept. of Elementary School Principals, . 1948. The principal and audio-visual education. Washington: .

Harvard

National Education Association of the United States. Dept. of Elementary School Principals, . (1948). The principal and audio-visual education. Washington: .

MLA

National Education Association of the United States. Dept. of Elementary School Principals, . The principal and audio-visual education. Washington: . 1948.