A theoretical situation-person-interactions model of learning and performance is presented, and applications of the model through the Instrumental Language Functions (ILF) approach with preschool normal and older variously handicapped children and adults are described. The model is graphically depicted and discussed according to such aspects as sensations which are basic to learning; sensations and long term memory (LTM); LTM and coding of sensation; LTM, coding, and short term memory (STM); and applications to general learning, memory, and language disturbances of retarded persons. The ILF approach is then discussed in terms of teaching subprocesses in concept learning (e.g., selective associations) and corresponding verbal expressions (e.g., differences and similarities), conceptual systems (e.g., which shape or color); and supporting children's emotional/motivational dispositions to build self-concept. Additional aspects discussed include influence of the ILF on coding in perception, analytic coding, skill learning, concept learning, STM, thinking and choosing acts, teaching, and learning of school subjects. Approximately one-third of the paper consists of examples of the ILF approach to teaching. (MC)