Arithmetic programming for students with mild mental disabilities requires a comprehensive perspective that includes attention to curriculum, instruction, and appraisal. Arithmetic computation should not dominate educational programming, but should be included in ways that are functionally relevant and meaningfully presented within a framework of problem-solving and applied experiences. The teaching of counting depends on an understanding of two basic concepts, one-to-one and many-to-one relationships. Instruction in these areas can take place in the forms of arrangements, patterns, and sets. A scheme referred to as the Interactive Unit makes instruction both systematic and flexible by organizing instruction, with four instructor inputs (manipulate, display, say, write) and four learner behavior changes (manipulate, identify, say, write). Within the schemata of the Interactive Unit, the teacher can develop an unlimited number of instructional activities and accompanying materials. In the use of arithmetic algorithms, it is important that the teacher become familiar with a variety of algorithms and correct only errors rather than the student's performance style. Other recommended practices include presenting addition as a process of joining sets, and using expanded notation to numerically represent each place value position. Examples are provided to illustrate how these methods can be used in the classroom. Eight figures are included. (JDD)