The Diagnostic Testing System (DX) is an integral system for developing and administering tests. The system can be utilized for testing in any subject matter, or any number of subject matters, at any level on scholastic or cognitive continuums. The major purpose of DX is to provide diagnostic data about the level at which a given student (or group of students) comprehend the material or concept being tested. Based on a one-disk or two-disk configuration of the Apple II with 48k of memory, the DX prepares an interpretive, diagnostic readout for the instructor which includes a record of the performance as well as a short narrative explaining the level at which the respondent comprehends the material tested. The DX package of eight subprograms includes test writing and editing systems, a test outcome feedback system, and a system for determining how many and which tests will be administered at a given time. DX, in its entirety, is designed so as to present a technically simple package which can be easily learned and put into operation by classroom teachers, including those without computer know-how. (PN)