This study investigated the stability of Wechsler Intelligence Scale for Children–Fifth Edition (WISC-V) scores for 225 children and adolescents from an outpatient neuropsychological clinic across, on average, a 2.6 year test-retest interval. WISC-V mean scores were relatively constant but subtest stability score coefficients were all below 0.80 (M = 0.66) and only the Verbal Comprehension Index (VCI), Visual Spatial Index (VSI), and omnibus Full Scale IQ (FSIQ) stability coefficients exceeded 0.80. Neither intraindividual subtest difference scores nor intraindividual composite difference scores were stable across time (M = 0.26 and 0.36, respectively). Rare and unusual subtest and composite score differences as well as subtest and index scatter at initial testing were unlikely to be repeated at retest (kappa = 0.03 to 0.49). It was concluded that VCI, VSI, and FSIQ scores might be sufficiently stable to support normative comparisons but that none of the intraindividual (i.e. idiographic, ipsative, or person-relative) measures were stable enough for confident clinical decision making.

Although the field of school psychology has made progress toward the use of tests and assessment practices with empirical support over the past 20 years, many school psychology practitioners still engage in what can be described as low-value value assessment practices that lack compelling scientific support potentially taking time and resources away from practices that have a demonstrated evidence-base. Why do school psychologists engage in questionable assessment and interpretive practices despite decades of discrediting scientific evidence? This article critically examines several plausible explanations for the perpetuation of low-value practices in school psychology assessment. It also underscores the importance of critical thinking when evaluating assessment and interpretation practices, and discusses practical recommendations to assist in advancing evidence-based assessment in school psychology training and practice as the field progresses well-into the 21st century. Impact Statement Many school psychologists engage in assessment practices that lack compelling scientific support potentially taking time, resources, and energy away from more effective practices. This article critically reviews reasons why these questionable assessment practices persist long after discrediting scientific evidence has been aptly presented. Recommendations are offered to promote the use of evidence-based practices and discourage the use of assessment methods lacking compelling empirical support in training and clinical practice.