Young children's writing skills are a critical component of their literacy development and are predictive of later reading achievement. Although recent research and policy reports identify the importance of supporting children's writing in early childhood, little research exists on how early educational settings promote children's writing development. The present study was designed to (1) validate a new measure for examining teacher writing supports in preschool classrooms and (2) use the measure to examine teachers' writing practice and their relation to child outcomes in a diverse group of preschool classrooms (N = 68). Psychometric analysis of the measure provided evidence of reliability, construct validity, and predictive validity for children's writing development in preschool. Observations included a comprehensive examination of the writing environment, environmental print, teacher modeling of writing, teacher scaffolding of child writing and independent child writing. Results indicated that teachers vary widely in their material and instructional supports of writing in preschool classrooms. In general, preschool teachers provided a variety of materials to support children's writing including a well-equipped writing center. Although many teachers were observed modeling or scaffolding writing, they used few strategies and those were typically characterized as low-level quality. (author abstract)