This study investigated the effects of a shared reading and guided play vocabulary intervention on the science vocabulary acquisition of children who were at risk for oral language difficulties. Fifty-five children from five preschool programs participated in a 15-day science vocabulary intervention. Children randomly assigned to the treatment group (n = 29) received explicit science vocabulary instruction through shared readings of informational science books and follow-up scientific investigations. Children in the business-as-usual group (n = 26) received typical instruction from their classroom teacher. Vocabulary knowledge was measured at pre- and posttest using two standardized vocabulary assessments and one researcher-developed science vocabulary test. Results of the researcher-developed test showed that the treatment group significantly outperformed the BAU group on explicitly taught science vocabulary words (p < 0.001). No significant differences were found between the two groups on measures of general vocabulary knowledge. Limitations and practical implications of this study are discussed.