1. The Development of Modern Education. Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1952, p. 615.
2. Science and Education Today, Supervision for Quality Education in Science (Washington, D.C.: United States Government Printing Office, 1963) p. 27.
3. Science and Education Today, Supervision for Quality Education in Science, p. 29.
4. A Seventh Grade Studies Ecology
5. American Association for the Advancement of Science. The New School Science, Miscellaneous Publication Number 63–6, 1962.