The main objective of this research was to analyze the impact of transcription skills of Spanish writers when writing an independently composed sentence within a writing-level design. The free-writing sentence task from the Early Grade Writing Assessment (Jiménez, in press) was used to examine the production, accuracy, speed, syntactic complexity, quality, and fluency of children with poor transcription skills (PTS). The results showed that there were significant differences between children with PTS and peers who had good transcription skills. The PTS group members were less accurate, slower, and less fluent or even dysfluent. Furthermore, their sentences were less complex and contained lower quality content. These results suggest that transcription skills play a crucial role in early written expression in Spanish, and poor transcription abilities hamper the acquisition and normal development of sentence composition.