This study examined the effects of a content-based shared book reading (SBR) intervention on receptive and expressive vocabulary outcomes of dual language learner (DLL) preschool children enrolled in two school districts in south Texas. Using SBR as the target of instruction, 50 preschool teachers and 298 preschoolers were randomly assigned at the class level to either a well-specified and scripted SBR condition or a comparison SBR condition. Children in the study were selected based on their scores on the school district administered and thereby archival Preschool Language Assessment Scales (Pre-LAS©) and determined to be at the Limited English Speaker (LES) level of English. Teachers in the intervention condition implemented the curriculum for 18 weeks in 5-day instructional cycles of about 20 minutes per day. Results revealed significant and robust effects on proximal measures of expressive and receptive vocabulary; whereas no significant effects on standardized measures were indicated. Limitations and implications are discussed. (author abstract)