A PRODUCTION SYSTEM FOR COUNTING, SUBITIZING AND ADDING11This paper presents a detailed description of production systems; there are several background papers that are required to fully understand the methodology and the particular substantive problems to which it is applied. For the general theoretical orientation, see Newell and Simon (1972); for the details of production systems and the rules of a production system interpreter, see Newell (1972). For the problems of cognitive development involving quantitative comparison, see Klahr and Wallace (1972); for quantitative processes data and theory, see Klahr (1972), and Klahr and Wallace (1973).