A study was conducted to inquire into serial and parallel relations of information processing. A hypothesis was derived from earlier studies, and it was assumed that serial processing exceeds parallel processing in time. A figure-type test was constructed with two items. The reliability of the measure was examined with the coefficient of alienation against a random criterion. Validity of the measure was examined with the goodness of fit of the relation structures. The subjects were 96 secondary comprehensive school students in Finland, and they were divided into 13-, 14-, 15-, and 16-year-old age groups. The analysis of processing consisted of a base line definition and the eigensystem solutions in each age group and between them. The results indicate a slight corroboration of the hypothesis with some exceptions. Thus the process of serial and parallel processing emphasizes the development of the control part or of the serial processing during time. A didactical process application was shown from the basis of the findings, and some shortcomings of educational theory construction are expressed. (Contains four tables, two figures, and two references.) (Author/SLD)