The analysis of response inconsistency is a crucial aspect of intellectual and clinical psychological assessment. Erratic patterns of failures and successes across and within particular domains qualify the measurement of intellectual potential and functioning. Although the interpretation of intertest scatter (inconsistencies between subtest scores) on intellectual tests has been elaborated on in the literature, intratest scatter (inconsistencies within specific subtests) is an underresearched area. Some approaches towards establishing a quantitative measure of intrasubtest scatter (ISS) have been developed, but most have proved clinically impractical or have produced inconsistent results. This article proposes a methodology of codifying ISS on the Wechsler Intelligence Scales to provide a measurement of inefficiency within subtests for individual subjects. In addition to systematizing and standardizing scatter measurement in clinical assessment, such codification will be useful in future research directed at discriminating groups based on inefficient performance across particular subtests. Applications and limitations in ISS interpretation for the various Wechsler instruments are annotated and discussed. (Contains 1 table.)