| Abstract: | This paper examines the limitations of standard scores of achievement tests commonly used in diagnosing learning disabilities. The consideration of these limitations is an important factor in attempting to decide whether a marked discrepancy exists between ability and achievemen, a requirement for the diagnosis of learning disabilities under Public Law 94–142. The phrase “standard score scale” is ambiguous because it can refer to both status score scales and developmental score scales. Unfortunately, many school psychologists seem unaware of the distinction between these two types of standard scores and the ramifications of this distinction. Many standardized achievement tests commonly used in the assessment of learning disabilities use status standard scores despite their severe limitations (noncomparability across grade levels and subjects, and failure to reflect changes in variability across grade levels). While developmental standard scores are to be preferred over status standard scores in diagnosing learning disabled children, their value is significantly lowered because they require greater growth for below-average students than for average or above-average students. Moreover, developmental scores are nonequal interval and they assume that subject matter is normally distributed within age or grade groups. Although we recommend the use of developmental standard scores over status standard scores, we urge that they be interpreted cautiously. |
