The difficulties that younger students experience in understanding concepts related to the use of variables in computer programming are examined through descriptions of two studies: (1) detailed case studies of six highly intelligent children--three fourth graders and three sixth graders--who learned to program in BASIC during 60 hours of instruction under the careful observation of research staff; and (2) a study in a regular classroom environment with 73 children in the fourth and sixth grades who had 12 two-hour hands-on lessons in programming. The programming textbook used in both studies taught the use of variables in the second half of the course, thus permitting comparison of the acquisition of programming concepts related to variables and the acquisition of concepts that do not involve variables. The results of the first study indicated that the fourth graders, in contrast to the sixth graders, were unable to learn the concepts associated with variables, even though they had understood the concepts without variables. The results of the second study indicated that the inability to understand concepts associated with variables was related more to the level of academic achievement than to grade level. It is suggested that four factors may explain the difficulties younger students experience in learning to use variables: (1) the level of abstraction in using variables; (2) the dynamic nature of the values of variables; (3) the degree of complexity in using variables; and (4) the level of reasoning required. Measures that may help to overcome the influence of these factors are suggested, and a 25-item bibliography is provided. (EW)