WHEN one begins to think about the application of learning principles to instruction, there is always one worthwhile question to be asked. What is to be learned? The responses to that question may fall into one of three general classes – intellectual skills, cognitive strategies, information, behavioural patterns, or attitudes. Of course, learning intellectual skills is of central importance to school learning. An intellectual skill makes it possible for an individual to respond to his environment through symbols, in which language and numerals represent natural objects of the environment. In other words, individuals communicate aspects of their experience to others by using such symbols. For most instructional purposes, the valuable distinctions among intellectual skills are discriminations, concrete concepts, defined concepts, rules, and problem-solving.