We asked why Spanish-monolingual children exhibit a weaker, slower-to-develop shape bias in word-learning contexts compared to English-monolingual children (Hahn & Cantrell, 2012). Ten English-monolingual adults and nine English-Spanish bilingual adults rated the perceptual similarity of items indicated by subsets of words from the English MCDI and Spanish MCDI, respectively. Consistent with previous research with similar methodology (Samuelson & Smith, 1999), words for shape-similar items predominated in the content of the English MCDI (47.72%; agreement: 70%, p < .05). Interestingly, words for shape-similar items also predominated in the content of the Spanish MCDI (56.67%; agreement: 70%, p < .05). Results suggest that the types of words that children learn play a less important role in the development of the shape bias than other proposed factors (e.g., syntactical regularities; Smith, 2000). Additional findings and implications for children with various language backgrounds will be discussed.