Participant Groups

The three groups of children were defined by exclusionary and inclusionary criteria. (1) Children in the Poor Reader group had standard scores below 90 (below 25^th percentile) on at least two of the four subtests: Word Identification and Word Attack in the Woodcock Reading Mastery Test – Revised Normative Update (WRMT^TM- R/NU) (35), Sight Word Efficiency and Phonemic Decoding Efficiency in the Test of Word Reading Efficiency (TOWRE) (36). A composite reading score was derived by averaging the standard scores of the four subtests in order to provide an overall estimate of reading ability. In addition, sentence-level reading ability was assessed by administering the reading fluency subtest in Woodcock-Johnson 3 Test of Achievement (37). (2) Children were included in the ASD group if they had a community-based clinical diagnosis of ASD that was confirmed by trained research staff using the Autism Diagnostic Observation Schedule (ADOS/ADOS-2) Module 3/4. To quantify the severity of the autism symptomatology, we converted participants’ ADOS scores to autism severity scores by using the calibrated severity metrics (38, 39). (3) Participants in the TD group scored within normal limits on the above standardized assessments of reading and ADOS, and had no first-degree relatives with reading disabilities or ASD (details in Supplement 1).