1. Ferster, C. B., Harvard Educational Review 28: 58 (1958).
2. New Approach To Teaching Intermediate Mathematics
3. Teaching machines;Harvard Graduate School of Educ. Assoc. Bulletin,1958
4. Pressey, S. L., School and Society 23: 586 (1926).
5. Pressey, S. L., School and Society 36: 934 (1932).