A study of the requisite processes for establishing diagnostic validity in reading was conducted in a seventh grade remedial reading classroom. The study's objectives were to (1) collect reliable diagnostic data on each student's performance in word recognition, oral reading, silent reading comprehension, and listening comprehension before and after the year's instruction; (2) document the teacher's instructional practices; (3) link outcomes with instruction; and (4) return diagnostic and outcome information to the teacher. On the basis of this information, the teacher made instructional adjustments for the next year's program in the areas of word recognition and oral reading. The diagnostic results for the following year showed improvement in student achievement in those areas. The results also indicated that an unobtrusive system for establishing diagnostic validity can be successfully introduced into the classroom. (Author/HTH)