The roles of (1) the sequence of instruction and (2) cognitive ability variables were investigated using a computer-assisted instruction (CAI) course on an imaginary science of "Xenograde systems." A rationale for an information processing task analysis was developed to overcome the deficiencies of other analytic methods. The new method was found to have good reliability of sequence determination. An index, called the hierarchical sequence conformity index (HSCI), was constructed for quantifying the degree of conformity of the sequence of a particular presentation to the sequence determined by the information processing task analysis. When the HSCI was used to study the effect of three cognitive abilities (induction, reasoning, and memory) the results indicated that: induction appeared to contribute to performance on disordered sequences of instruction, reasoning ability affected performance on self-selected sequences, and memory appeared to have no effect on performance. Since selection of one's own sequence did not produce an increase in performance or interest, a predetermined hierarchical sequence may achieve the desired instructional goal as efficiently. (Author/JY)