Classroom boredom in the secondary mathematics classroom is a problem that can be addressed from knowledge of the intrinsic motivational variable of "interestingness." The lack of a theoretical model of interest is an obstacle in research that investigates this variable. This paper describes the three stages in the development of a model of interest. The first stage involved the development of a preliminary model according to the current research literature on interest. Working from the social ecological research orientation of (R. H.) Moos (1976, 1979) that emphasizes the importance of social perceptions as the key to manipulating an environment, the second stage included an elaboration on the initial model using naturalistic techniques to better understand student perceptions of interest in the mathematics classroom. In the third stage, a survey instrument was developed. Data was collected and quantitatively analyzed to assess the tenability of the model developed through stages one and two. Participants in the study consisted of 350 high school students from 3 different high schools in the Santa Barbara (California) area. The sample was composed of 147 boys and 188 girls, 30% of whom were not Anglo-American. Students responded to a Likert-type survey consisting of 45 items representing 7 different scales identified as the following: personal interest; situational interest; meaningfulness; involvement; group work; puzzles; and computers. Factor analysis, LISREL analysis, and correlational analysis were applied to the data. Results of the various analyses identified two general scales for personal interest and situational interest (SI) and five subscales for SI. In addition, the correlational analyses lent support to the conceptual distinction made between catching and holding interest. (Contains over 60 references.) (MDH)