Emergent writing is a key component of early literacy development and contributes to later school success, yet it receives little attention in most preschool classrooms. This paper presents results of a quasi-experimental study of a teacher professional development package that included writing as one of four focal areas. The study was conducted in 15 Head Start classrooms located in the U.S. state of Hawaiʻi. The participants were 39 lead and assistant teachers and 240 children. Intervention teachers had higher quality writing environments and overall classroom environments, while intervention children showed better outcomes on emergent reading and upper case letter knowledge. Emergent writing was assessed only in the intervention group, where children showed large gains along with changes in code-related skills needed for invented spelling. Results are discussed in terms of recommended practices for early writing instruction and teacher professional development. (author abstract)