To learn more about the specific nature of the teaching and learning problems involved, researchers conducted a clinical study of 20 high school students enrolled a BASIC course. Investigators presented each student with a sequence of eight programming problems, ranging from easy to difficult. They asked questions to track student thinking and intervened in student difficulties with graduated levels of assistance. A coding system was used to record the type of difficulty students encountered, the amount of help needed, and the correctness of solutions. Experimenters noted whether errors were omissions of a necessary element, inappropriate migrations of an element from one command to another, errors in sequencing the elements, or other mistakes. Data analysis provided information about loci of difficulty in three aspects of programming behavior: attitudes, knowledge base, and problem-solving strategies. Inadequacies in students' knowledge base about BASIC were revealed, with most errors occurring at the level of application. Findings suggest that programming instruction might place greater emphasis on encouraging students to prompt themselves with strategic questions about problematic situations, on helping them achieve more consolidated knowledge of the details of computer languages, and on addressing attitudinal and confidence factors in programming. (32 references) (Author/MES)