The expert systems are designed to imitate the reasoning of a human expert in a content area field. Designed to be advisors, these software systems combine the content area knowledge and decision-making ability of an expert with the user's understanding and knowledge of particular circumstances. The reading diagnosis system, the RD2P System (Reading Difficulties--Diagnosis and Prescription) based on an expert system shell, guides teachers to an understanding of the possible problems underlying a student's reading difficulties and suggests possible instructional methods to solve those problems. Advantages of the expert systems are that they (1) allow an organization to place untrained staff in key decision-making positions, (2) free professionals from information processing overload so that they can provide services that only humans can offer, (3) bring the best and most expensive of expertise to bear on a problem, (4) are designed so as not to overlook remote possibilities, (5) can be easily updated as new knowledge becomes available, (6) can be used for teaching purposes, and (7) raise questions about the field of expertise and can pinpoint areas where additional research is needed. (Teacher observation data are appended.) (EL)