Imagery use in high school mathematics classrooms was studied. A visual image was defined as a mental scheme depicting visual or spatial information, but this definition was not spelled out to teachers or students, in order to learn what they meant by the concept. Subjects were 13 high school teachers and 54 of their students interviewed over 3 years. Images used by the students were classified in the following categories: (1) concrete, pictorial imagery; (2) pattern imagery; (3) memory images of formulae; (4) kinesthetic imagery; and (5) dynamic imagery. Images were used as prototypes, as metaphors, and as metonymies (i.e., a subcategory or submodel used to comprehend the category as a whole). Concrete imagery was particularly used in these ways. Pattern imagery, in which concrete details are disregarded and pure relationships are depicted in a visual-spatial scheme, was used much less often. Teachers were classified into three groups, depending on their use of imagery. Very visual teachers often were unaware of difficulties some students had with a visual approach, and non-visual teachers similarly ignored the benefits some students could derive. However, teachers in the middle group, who used some visual aspects, but valued abstraction and generalization, were able to use imagery most effectively. One of four figures illustrates a visual problem solution. (Contains 11 references.) (SLD)