In the present study we examined the contributions of transcription and foundational oral language skills to written composition outcomes in a sample of kindergartners. Two hundred and eighty-two kindergarten students from 49 classrooms participated in this study. Children's writing-related skills were examined using various tasks. Latent structural equation modeling was used to test the hypothesis that transcription moderates the relation between foundational oral language and compositional productivity and quality for kindergarten writers. This hypothesis is one possible manifestation of the Developmental Constraints Hypothesis (DCH). In support of the DCH, transcription had a strong constraining effect on both composition quality and productivity. Additionally, transcription moderated the relation between foundational oral language skills and composition quality, although the moderation was negative. There was no signification moderation of transcription on the foundational oral language-composition productivity relation. Implications of the findings and future directions are discussed including challenges assessing composition in young, beginning writers. [This paper was published in "Early Childhood Research Quarterly" v67 p227-238 2024.]