This paper describes a paradigm for tutorial systems capable of automatically providing feedback and hints in a game environment. The paradigm is illustrated by a tutoring system for the PLATO game "How the West Was Won." The system uses a computer-based "Expert" player to evaluate a student's moves and construct a "differential model" of the student's behavior with respect to the Expert's. The essential aspects of the student's behavior are analyzed with respect to a set of "issues," which are addressed to the basic conceptual constraints that might prevent the student's full utilization of the environment. Issues are viewed as procedural specialists that "wake-up" or become active when an instance of an issue manifests itself in a move. These issue specialists help the Tutor isolate what to comment on. The intent of the system is to transform a "fun" game into a productive learning environment without altering the student's enjoyment. (Author)