The purpose of this study was to design a unit on percent for adult remedial students based on the principles of Piaget's theory and to evaluate the effectiveness of the unit as a means of improving one characteristic of formal operations, the ability to use porportion. The subjects consisted of 89 undergraduate remedial mathematics students at a branch of the City University of New York. Results indicate that there seems to be a relationship between learning percent and improving the ability to use proportions. Moreover, it would seem that an instructional unit can be developed which implements some of the heuristic principles of Piaget's theory and which simultaneously improves one characteristic of formal operations and develops basic mathematical principles. In addition, it appears that Piaget's theory can be successfully applied to the instruction of adult remedial students and that this theory can be implemented in an actual classroom situation involving instructors of remedial mathematics courses. (Author/MK)