1. A Comparison of five Piaget-type tasks under two modes of presentation. Unpublished doctoral thesis, The University of Iowa, Iowa City, Iowa, 1973.
2. Measurement of logical thinking: An electronic equivalent of Piaget's first chemical experiment
3. An investigation of two formal-operational schemata in adolescents enrolled in ISCS classrooms
4. An investigation of two formal operational schemata in adolescents in the ISCS classrooms of three selected teachers. Unpublished doctoral thesis, The University of Iowa, Iowa City, Iowa, 1972.
5. & The growth of logical thinking from childhood to adolescence. New York: Basic Books, 1958.