With reference to data from a Swedish investigation into learning difficulties in mathematics, an analysis is presented of models and taxonomies applied to special education problems. The author suggests that such developmental cognitive theories as those of J. Bruner, J. Piaget, and R. Gagne are suitable as a starting point for a taxonomy in mathematics for low achievers but contain inconsistencies. Proposed is a three dimensional model which relates the child's stage of development, instructional objectives and activities, and mathematics content categories. (Author/DB)