Base rates of low achievement scores in young adults: implications for specific learning disability assessment.

Background: Specific learning disability (SLD) is a high-incidence diagnosis, with academic skill deficits at its core. Diagnostic models for SLD vary but they generally require data from norm-referenced achievement tests. Multivariate base rates for low scores on such tests have not been examined in young adults.

Methods: The young adult (ages 18-29) group from the Woodcock-Johnson IV (WJ-IV; 2014) normative sample (N = 1330) was used. We calculated base rates for low scores on the 11 subtests of the Standard Battery of the WJ-IV Tests of Achievement. We also calculated base rates for discrepancies between participants' General Intellectual Ability scores and their achievement subtests.

Results: Low achievement subtest scores were very common; most participants had at least one standard score below 90, and almost half had at least one score below 85. Achievement scores that were discrepant from ability scores were also common; most participants had at least one score that was at least 1.0 SD below their ability estimate, and among high-ability subgroups, discrepant achievement scores were extremely common.

Conclusions: Normative and relative low achievement subtest scores are common in the general population of young adults. SLD diagnosis in young adults should require objective evidence of other criteria being met, such as trouble initially acquiring academic skills in childhood, current functional impairment in educational or occupational settings, and rule-outs of other possible causes of low achievement test scores.