Acquisition of an argument structure may be affected by the diversity of lexical types that appear in that structure (Conwell et al., 2011; Yang, 2016). Seventy-two 5- and 6-year-old English-speaking children completed a learning study where they were exposed to a novel argument structure and then tested on their ability to comprehend it. The number of verb types heard in the learning phase did not predict comprehension at test. However, learning with only full noun phrase arguments resulted in lower comprehension of the structure, particularly with pronouns. Hearing pronouns during learning supported comprehension of all argument types at test. These results indicate that pronominal arguments support argument structure learning by providing multiple cues that can facilitate thematic role assignment.