Presented is the Illinois Regional Resource Center's Manual for Diagnostic Teachers which is designed to provide a model for assessment, individualized educational planning, optimal placement, and short and long range follow-up of children (3-21 years old) with unexplained learning problems. Section 1 provides an introduction to the Illinois-Regional Resource Center Diagnostic Teaching Model (IRDTM) with sections on the model's purpose, target population, and 11 features of the IRTDM (such as the emphasis on diagnosis rather than remediation; the delivery of both on-site and in-classroom services; and a holistic approach which covers the motor, sensory-perceptual, academic, speech/language, social-emotional, and self-help domains). Section 2 makes up the bulk of the document with flow charts on the five phases of the model--initial information gathering, on-site or in-classroom diagnosis, program development and testing, transition, and follow-up. Among the exhibits presented in section 3 are samples of a referral form; follow-up form; case contact record; formal and informal test score worksheets; teacher, parent, and child follow-up records; informal and formal evaluation data summaries, and federal reporting form. A hypothetical case study for the IRDTM is given in section 4 which provides examples of the written materials produced by the diagnostic team during the diagnostic, program development, and testing phases. Among appended materials in a final section are regional resource center job descriptions; suggested qualifications for diagnostic teachers; a list of consultants available to the regional resource center team; and bibliographies of diagnostic tests, instructional materials and equipment, and behavioral checklists. (SBH)