This large-scale, experimental study aimed to (a) describe the extent to which teachers of preschool children at risk for reading difficulties make references to print during whole-class, shared-book read alouds and (b) empirically test the extent to which participation in professional development influences teachers' frequency of references to print during shared read alouds across the academic year. Eighty-five preschool teachers working in targeted-enrollment preschool programs were randomly assigned to receive professional development aimed at increasing their use of print referencing or to a comparison condition involving alternative training; all teachers implemented a shared read aloud program in their classrooms. Implementation was documented via twice-monthly videotaping of shared read aloud sessions. Videos were coded for the frequency of print references and analyzed using latent growth curves. Despite considerable variability in teachers' use of print referencing, findings showed sustained, meaningful changes in teachers' use of print referencing with results favoring those who experienced the experimental professional development. Implications concerning effective professional development for supporting preschool children's emergent literacy skills are discussed. (Contains 3 tables and 4 figures.)