1. Interaction. Teacher's Guide, Preliminary Edition. Science Curriculum Improvement Study, D. C. Heath & Co., Boston, 1967, p. 2.
2. An evaluation of certain cognitive aspects of the material objects unit of the science curriculum improvement study elementary science program
3. An examination of the ability of first graders from the science curriculum improvement study program to describe an object by its properties
4. et al., Concepts in Science, Harcourt, Brace & World, Inc., New York, 1966.
5. Interaction. Teacher's Guide. Preliminary Edition. Science Curriculum Improvement Study. D. C. Heath & Co., Boston, 1967, p. 13.