Children with specific language impairments (SLI) have difficulties in producing written text. It was hypothesised that the constraints on writing in children with SLI were similar to typically developing younger children with the same level of vocabulary knowledge. Twenty-three children with SLI (aged 10:5) were matched with 23 children for chronological age (CA) and 23 children for vocabulary levels (VC). Children with SLI performed significantly below their CA peers but not their VC peers on all aspects of writing including spelling. Regression analyses indicated that written text measures of spelling errors and oral language measures of vocabulary were significant predictors of writing products for both the children with SLI and their VC peers. This highlights the importance of oral and written language for the quality of children's written text and indicates that the writing of children with SLI was commensurate with their vocabulary and spelling levels. The results point to the role of both phonological and non-phonological processes in written text production in struggling writers.