A microcomputer-based system that approaches four goals of an ideal diagnostic test is at an advanced stage of development by the College Board and the Educational Testing Service. The goals are not only to test a pupil's ability or knowledge, but also: 1) give feedback; 2) provide information about an individual pupil's weaknesses and strengths; 3) identify misconceptions; and 4) provide clues as to the reasons underlying mistakes. The diagnostic testing program includes instruments in three areas: 1) mathematics; 2) written skills; and 3) reading and study skills. Designed for the college first-year student, the material covers precollege skills. Instead of grades or scores, the system provides descriptions of each student's performance with computer-generated narrative reports; separate reports to students and instructors; analyses of why mistakes are made; and instructional suggestions. The exercises are in sessions of about 45-minutes apiece. The field test material includes about 19 sessions: seven in written communication skills; six in reading and study skills, and six in mathematics. The set will eventually have about 28 units. The first phase of field testing is finished in two state universities, two community colleges, and a high school. Subsequent field testing phases will emphasize instructor reactions and usefulness of the materials for instructional diagnosis and planning. Seventy-one per cent of the students said that they prefer to take a test by computer rather than by paper and pencil, and additional 16% have no preference. Students had no difficulty using the computer, even if they had never used one before. Ninety-nine per cent describe the instructions for computer use adequate. The students work long and attentively. According to teachers and students, face validity is high. Six features are variables for significant exploration: 1) challenge and probe; 2) sustained engagement in a task; 3) feedback and second try; 4) student-generated response; 5) special-purpose response modes; and, 6) teacher-test interaction.