A mathematics curriculum for moderately and severely retarded and autistic students and adults should possess 10 necessary characteristics, including provision for instruction based on assessment results, stress on functional application, focus on generalization of skills, and specific criteria for mastery of each skill. The functional but developmentally based program described was organized around 47 skills in two sections: the perceptual correspondence and the numerical correspondence curricula. Perceptual correspondence deals with the student's ability to understand separate objects (discontinuous quantities) and includes concepts of "one/many" and "more." Numerical correspondence covers the development of qualitative and numerical seriation and includes functional addition, subtraction, multiplication, and division. Language related concerns in the development of the curriculum included students' tendencies to answer affirmatively to yes or no questions, and difficulties with understanding the words "one,""amount," and "enough." Sequences of instruction were coordinated with theories of J. Piaget. Specific teaching techniques for each skill level were developed using generalized materials and examples. Differences were noted between autistic and retarded students in performing mathematics curriculum tasks. The curriculum has also been effective in teaching functional mathematics to elementary students with mild retardation and learning disabilities. (CL)