In 1966, Patrick Suppes boldly conjectured, “One can predict that in a few more years, millions of school children will have access to what Philip of Macedon enjoyed as a royal prerogative: the personal [Page 422]services of a tutor as well-informed and responsive as Aristotle” (p. 207). Soon afterward, Suppes and Mona Morningstar published studies showing benefits for learners studying elementary school arithmetic and college-level Russian-language courses using an adaptive drill-and-practice software system. It selected content based on an individual’s history of progress and principles of operant psychology, particularly schedules of reinforcement. Such adaptive software set a cornerstone for intelligent tutoring systems (ITSs), that is, software designed to instruct a learner to develop knowledge and skills at least as well and in no longer time ...