Learning to program involves developing an understanding of two hierarchies of concepts. One hierarchy consists of data and extends from very literal data (which represents only itself) to very abstract data incorporating variable values in complex interrelationships. The other hierarchy consists of the operations performed on the data and extends from straight, linear sequences to loops, internal tests, and branching structures. Grasping the successive concepts in these hierarchies requires development of successive cognitive skills. If the best tools for delivering instruction in programming are to be designed, the designer must be conscious of both the developmental level of the students being taught and the difficulty levels of the specific programming tasks to be accomplished. A list of 35 documents suggested for further reading on the subject is supplied, as an addition to the bibliographic material cited in the text. (Author/PGD)