Longitudinal results for a randomized-controlled trial (RCT) assessing the impact of increasing preschoolers' attention to print during reading are reported. Four-year-old children (N = 550) in 85 classrooms experienced a 30-week shared reading program implemented by their teachers. Children in experimental classrooms experienced shared-book readings 2 or 4 times per week during which their teachers verbally and nonverbally referenced print. Children in comparison classrooms experienced their teachers' typical book reading style. Longitudinal results (n = 356, 366) showed that use of print references had significant impacts on children's early literacy skills (reading, spelling, comprehension) for 2 years following the RCT's conclusion. Results indicate a causal relation between early print knowledge and later literacy skills and have important implications concerning the primary prevention of reading difficulties.