Preschool children with neurotypical development (ND) trained on sentential complements (“X thinks/saysthat”) improve their Theory of Mind (ToM) performance. Can complementation training also enhance ToM in children with Autism Spectrum Disorder (ASD)? Thirty-three children with ASD (Mage= 8;11) and 20 younger ND peers (Mage= 4;3) were trained on sentential complements (4–6 weeks, 2–3 times per week, via the DIRE i-Pad App). Pre-training and post-training comparisons show that (1) training boosted both complementation and ToM performance across groups; (2) improvements remained 4–6 weeks after training ended; (3) participants with milder ASD symptoms made most gains. Training on sentential complements thus seems beneficial for addressing ToM difficulties in children with ASD, especially those with milder symptoms.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10803-022-05507-0.