The development of computer-based instruction will be greatly facilitated by the use of an effective and efficient design model. Five components of such a model are: (1) the objective; (2) the content; (3) the questions; (4) the boundaries; and (5) the entry skills. A good objective describes either something observable that learners do, the conditions under which they do it, and the standard of an acceptable performance; or an observable product that learners produce, the conditions under which they produce it, and the standards of an acceptable product. The content may take many forms--definition, description, generalization, principle, rules, and others. Learner processes will vary according to the content type, i.e., a rule-using task requires the learner to state the rule and then to apply it to a previously unencountered example of the class of problems for which the rule is intended. The questions enable the student to interact with the content and they test the student's mastery of the objective. Questions may be stated in interrogative (Which one is green?) or imperative form (Write the sum of three numbers), and three kinds of feedback can be provided: knowledge of results (KR), knowledge of correct results (KCR), or KCR with advancement to next problem or question. The boundaries define the area the objective covers; one part of that area is the domain (stimulus or display), the other is the range (answers to the questions). Entry behaviors are stated for two reasons: to ensure that nothing is omitted and that there are no overlaps between old knowledge and new instruction, and to weed out students who lack prerequisite skills. Examples are provided for each of the five model components. (JB)