This study attempted to discover some parameters in terms of mental age at which young children, ages five through eight, begin to utilize effectively their mental imagery in the learning process. Using Piaget's principles of conservation as a learning task, subjects were taught in one of two groups: Group one was instructed in conservation concepts by use of concrete example, in which case they were allowed to see, handle and manipulate materials as they underwent transformations. Group two received identical instruction but were called upon to use their mental imagery to visualize the materials undergoing transformations. Based upon the administration of the California Test of Mental Maturity and a pretest, sixteen non-conserving subjects from the kindergarten, first, second, and third grades, making a total of sixty-four subjects, were grouped by matching I.Q.'s to receive four periods of instruction in the principles of conservation. Following instruction each subject was individually administered a posttest and a test of extinction. The test of extinction was designed to measure the degree or depth of conservation acquisition achieved by each subject. A statistical analysis of the data indicated that while children of ages five through eight were able to learn conservation through both methods of instruction, mental age and I.Q.'s were not determining variables. No learning curve based on mental age or I.Q. was discernible. It was strongly indicated, however, that boys resist extinction of conservation principles better when taught through concrete example than they do when taught through mental imagery. Girls utilize mental imagery in acquiring conservation better than do boys of the same age, and as well as boys who learn by use of concrete illustration. Girls' use of mental imagery in the learning process appears to be equal to their use of concrete example.