Information processing speed as a predictor of IQ in children with and without specific language impairment in grades 3 and 8

• We examined whether processing speed predicts IQ in children with SLI and TD.
• We examined whether this relationship between processing speed and IQ changes over time.
• Slower processing speed predicted a lower IQ across groups on a timed IQ measure.
• Relationship between processing speed and IQ stayed stable over time across groups.

PurposeThis study investigated (1) whether nonlinguistic processing speed predicts nonverbal IQ in TD children and children with SLI and (2) if the proposed relationship is different at two time points.MethodThe participants consisted of a subset of a longitudinal dataset, 55 typically developing children and 55 children with SLI. Children completed four nonverbal speed tasks and four subtests of the WISC-III. The WISC-III subtests requiring timed and untimed responses were examined separately.ResultsLinear mixed model analyses indicated that in both groups, processing speed predicted nonverbal IQ subtests that reward speedy responses, but not IQ subtests that do not. The relationships between processing speed and IQ with speed bonuses did not differ at grades 3 and 8, and these relationships also were not significantly different in children with SLI and their TD peers.ConclusionsThe results suggest that the presence of processing speed limitations in many children with SLI raises questions about the utility of timed nonverbal IQ measures as tools for diagnosis of SLI. Future studies should investigate other cognitive assessments that could be used as inclusionary criteria for SLI.Learning outcomes: The reader will be able to (1) describe the relationship between processing speed and nonverbal IQ in children with TD and SLI and (2) discuss problems using an IQ criterion to diagnose children as having SLI.