The author stresses that diagnosis is desirable only when it leads to special education intervention. Diagnosis in a service vacuum is seen to be unnecessary and frustrating for parents and teachers of handicapped children. It is also emphasized that assessment of intraindividual differences is more valuable than that of interindividual differences and that IQ score has limited value in providing information about a child's strengths and deficiencies upon which prescriptive teaching programs can be developed. Finally, it is suggested that familiarity with the concepts and techniques of criterion-referenced testing is helpful for teachers to construct informal tests for classroom uses and that criterion-referenced testing is also closely integrated with self-paced, individualized instruction. (Author/SBH)