One important theoretical consideration too often neglected in educational research is that of opportunity cost. The multimilliondollar Tennessee class-size study, while admirable for its random assignments and statistical punctiliousness, did not adequately address theoretical questions concerning unanalyzed opportunity costs. Could there be alternative, more reliable, and more cost-effective ways of achieving similar or higher gains? If, for example, an important advantage of smaller class size is more interaction time between student and teacher, are there alternative, less expensive policies for achieving more interaction time and still greater student gains? In other words, the Tennessee STAR study did not hazard a clear and detailed theoretical interpretation and generalization of its own findings. If it had, the state of California, basing its policy on the STAR study, might not have spent $5 billion in an unsuccessful effort to im¬prove achievement simply through smaller class size.