This study explored 3- and 4-year-old children's development of scientific vocabulary from participation in repeated interactive read-aloud events and retellings of three informational picture books about light and color, followed by hands-on science activities. Thirty-two children attending a YWCA preschool were matched by age and general vocabulary knowledge and randomly assigned to a retelling or no retelling condition. Repeated measures ANOVA of pretest and posttest scores on a free recall target vocabulary test revealed significantly higher scores for 4-year-olds, those with higher vocabulary knowledge, and those who retold the books. Children used significantly more target words across the three retellings. (Contains 5 tables.)