Both the background of computer-assisted instruction (CAI) systems in general and the requirements of a computer-aided learning system which would be a reasonable assistant to a teacher are discussed. RASCAL (Rudimentary Adaptive System for Computer-Aided Learning) is a first attempt at defining a CAI system which would individualize the learning environment by identifying the proper roles of the teacher and the computer. RASCAL replaces the prepared set of frames that is at the core of many CAI systems with a "tree structure" which approximates the steps a teacher would follow in assisting a student in the solution of a problem. The branches of the tree are interactively constructed, either by the teacher or by the computer, from a broad set of alternatives defined by the teacher. The computer must generate problems for the student, decide when the student is ready to proceed to more difficult concepts, present instruction frames or review material, manage and manipulate files, and identify problem areas for the teacher. The teacher must tell the computer the student's present state of advancement and capability, specify the type of problems to be presented to the student, and construct the branches to be followed in assisting the student to answer the problem. (JY)