Objectives: To test whether ToM mediates the relationship between early grammar abilities and adolescent functioning (social and communication) at ages 16-18 in a longitudinal cohort of youth with high-functioning ASD (IQ > 70).
Methods: 35 children with ASD (8 Asperger’s syndrome, 27 high functioning autism; M=30, F=5) were recruited at ages 4-6 as part of a larger cohort study of high functioning ASD, with psychometric testing performed every 2 years. Grammatical ability was measured using the Test of Language Development-2 at ages 6-8; ToM at ages 13-15 years was measured using the “Reading the Mind in the Eyes Test”. Outcome scores at ages 16-18 were measured using the Vineland Adaptive Behaviour Scale, Social and Communication domains. Regression analyses tested for mediation according to the Baron-Kenny model.
Results: Grammar was significantly associated with VABS Communication and Social scores (r = 0.76 and 0.44, p < 0.001), and with ToM scores (r = 0.65, p < 0.001). ToM predicted a significant amount of variation in Communication and Social scores (r =0.67 and 0.40, respectively, p < 0.01). ToM partially mediated the association between grammar and VABS Communication scores (Sobel test = 2.07, p < 0.04), but not between grammar and Social scores (Sobel test = 0.77, p < 0.44).
Conclusions: Grammar and ToM are strongly associated over time in children with high-functioning ASD and are important predictors of adolescent adaptive functioning. ToM does not appear to mediate the relationship between early grammar and later social functioning.