Assessment of school aged youngsters is an omnipresent decision making activity; intervention planning is an important component of this decision making. A child's strengths and weaknesses may be useful indicators on which to plan instructional programs; unfortunately, they often are not identified as a result of general assessment practices. Diagnostic testing offers some advantage in this regard in that a child's test performance is evaluated relative to tentative hypotheses about learning problems. In practice, the principles of diagnostic testing may be applied to many different types of behaviors samples. A procedure for analyzing word recognition samples relative to applied information in word-attack skills is presented. The process involves administration of a formal reading test with subsequent stages of error analysis and teaching. (Author/DB)