This project was an empirical investigation of predictions derived from a theory by Piaget concerning the development of intelligence. In particular, three content areas were to be studied, making use of group testing procedures and special statistical techniques for analysis. In general, it was concluded that the group testing situation could be used experimentally with systematic variation of the content of items. Piaget's theory was used as the basis of this variation and certain predicted results were obtained. Some specific suggestions for further studies arose from the results of this study.