This study examines the Peabody Picture Vocabulary Test-IIIB (PPVT-IIIB) performance of 130 adults identified as struggling readers, in comparison to 175 third-grade children. Response patterns to the items on the PPVT-IIIB by these two groups were investigated, focusing on items, semantic categories, and lexical features, including word length, word class, and word frequency. The score distributional properties of the two groups were different, but there were similarities and differences found in different response patterns. Analyses of word length, word class, and word frequency in the two groups' performance resulted in counterintuitive findings for the adult participants. The struggling adult learners' vocabulary repertoire might have been shaped by their real-life experiences rather than formal schooling. Implications and future research directions are discussed.