Stability of the intelligence quotient-language quotient relation: is discrepancy modeling based on a myth?

Diagnostic and service eligibility decisions are often made on the basis of the relation between assessments of cognitive ability and assessments of language ability. A discrepancy between cognitive and language performance, with cognition being higher, is thought to be a positive predictor of ability to benefit from intervention. This triage model assumes reasonable stability of cognitive and language measures over time. We evaluated the stability, over 1- and 2-year periods, of the relation between a cognitive measure and two language measures. We examined whether the cognitive-language relation for these measures changed significantly over time and whether children remained in the same service eligibility category, based on the discrepancy model, over time. Results indicated substantial changes in the cognitive-language relation over time. Children's eligibility for service, based on the discrepancy model, also fluctuated greatly over time. We conclude that a discrepancy model of triage based on broad cognitive and language measures is not an effective means of determining who should receive service. Alternative triage methods were presented.