In this study we evaluated the predictive validity of conceptual scoring. Two independent samples of Spanish-speaking language minority preschoolers (Sample 1: N = 96, mean age = 54·51 months, 54·3% male; Sample 2: N = 116, mean age = 60·70 months, 56·0% male) completed measures of receptive, expressive, and definitional vocabulary in their first (L1) and second (L2) languages at two time points approximately 9–12 months apart. We examined whether unique L1 and L2 vocabulary at time 1 predicted later L2 and L1 vocabulary, respectively. Results indicated that unique L1 vocabulary did not predict later L2 vocabulary after controlling for initial L2 vocabulary. An identical pattern of results emerged for L1 vocabulary outcomes. We also examined whether children acquired translational equivalents for words known in one language but not the other. Results indicated that children acquired translational equivalents, providing partial support for the transfer of vocabulary knowledge across languages.