The objective of this study was to determine if the Annehurst Curriculum Classification System (ACCS) learner characteristics and curriculum materials classifications among elementary mathematics students, can be used as the dimensions of an aptitude-treatment interaction analysis. The subjects were 34 fourth and fifth graders in three open-space individualized mathematics classrooms. The pupils and their materials were classified high or low by ACCS criteria on the ten categories: experience, intelligence, motivation, emotion-personality, creative, social and verbal expression, visual perception, auditory perception, and motor perception. Achievement scores on summative exams, attitude scores as measured by a semantic differential, and number facility aptitude scores were collected. Using a general linear regression technique, the ATI's were tested. When only ACCS variables were the dimension of the ATI analysis, no significant interactions were found. When number facility was used as the aptitude and material classification the treatment, there were significant disordinal interactions for the ACCS categories of experience and emotion-personality. (Author/GA)