The IMOD describes how people understand and become competent in the occupational world. The interaction of a person with his/her occupations in the context of the environment across time results in systematic change in occupational behaviors. The three variables of interactional occupational development are: occupational behavior (interaction of person and occupation in the environment), time, and interaction between occupational behavior and time The IMOD is depicted as three circles, composed of two intersection circles (person and occupation) inside a larger circle (environmental context). An expanding arc represents growth and development as a backdrop. Occupational behaviors are presented by circles shown at points in time, with the one on the right larger than the one on the left, indicating growth and development over time. The principles that govern occupational development and predict the course of occupational development are:
(1) staged continuity which is influenced by ages and stages of human development, the development of life course occupational repertoire as a continuous and cumulative of occupational behaviors,
(2) multiple determinicity which includes many factors in determining occupational development, and
(3) multiple patternicity, where occupational life course is marked by periods of both growth and decline, expansion and contraction, with occupations emerging at various points throughout life.
Stage continuity implies that children have a continuous, innate tendency towards doing or being occupied. The other two principles should be considered to assess the components of occupational behavior (e.g., cognitive, affective, and physical). Canadian Occupational Performance Measure can be used to identify the occupations that the child can do, did in the past, does now, and desire to do, or expected to do. Occupational therapists also identify the occupational opportunities, support and barriers in the environment. When incongruence between occupational competence and development status is identified, therapists may consider splinter skill, which is the evidence of the influences of interactionism on occupational development. Interventions, e.g., performance-based treatment, environmental adaptation or modifications, are used to improve children’s occupational competence and occupational development.