Why aren scores from CASL and, for example, CELF-3 comparable?
Score differences between tests can occur for numerous reasons: (1) The two tests are not measuring the same construct; (2) The construct is not being measured in the same way; (3) The standardization samples on which the tests are based are not the same. In the case of CASL and CELF-3, all of the above apply. Chapter 4 in the CASL manual tells you specifically what each CASL test is measuring and how to interpret results. A big difference between CASL and CELF-3 is the standardization samples. The CELF-3 technical manual states that “no examinee in the standardization sample was receiving language therapy or had a diagnosed or identified language disorder.” This means that the CELF-3 norms are based on children not identified as special education students. CASL, like all AGS tests, is standardized on subjects with a full range of ability. Special education students are included in approximately the same percentages that they occur in the population. You might be interested in reading
