Approximately 75% of children diagnosed with Autistic Spectrum Disorder (ASD) are significantly language impaired. While many learn a reasonably-sized set of object words, few master the relational terms (verbs and prepositions) that are the architectural centerpiece of the sentence. Though learning relational terms poses difficulty even for typically developing children, these words are differentially harder for children with ASD. This research is the first to ask why. Three studies examine the abilities necessary to learn verbs and prepositions. Studies 1 and 2 ask whether children with ASD have greater problems dissecting events into the foundational units and categories that underlie relational term learning (i.e., the path or where the object moves, and the manner or how the object moves through space) than do typically developing children. Study 3 focuses on tools known to assist in mapping from these basic categories onto words. Are children with ASD able to use information about a speaker's social intent to discover which event components are labeled by a particular word? Finally, this dissertation offers an exploratory correlational analysis designed to assess the joint impact of conceptual abilities and mapping (social understanding) as predictors for relational term learning in the two populations. Thirty-four 3- to 6-year-old children (17 with ASD) participated in the studies. Despite some methodological difficulties with the conceptual tasks, results suggest that the strongest correlate of relational vocabulary size in typical children was conceptual, while the strongest for children with ASD was social understanding. These findings extend prior research by noting the strong relationship between the ability to read social intent and relational term learning. They also suggest that for children with ASD, difficulty understanding the intentions of others is a primary problem that blocks the road to full language competence.