Purpose: Little is known about the relationship between sentence production and phonological working memory in school-age children. To fill this gap, we examined how strongly these constructs correlate. We also compared diagnostic groups' working memory abilities to see if differences co-occurred with qualitative differences in their sentences. Method: We conducted Bayesian analyses on data from seven- to nine-year-old children (n = 165 typical language, n = 81 dyslexia-only, n = 43 comorbid dyslexia and developmental language disorder). We correlated sentence production and working memory scores and conducted t tests between groups' working memory scores and sentence length, lexical diversity, and complexity. Results: Correlations were positive but weak. The dyslexic and typical groups had dissimilar working memory and comparable sentence quality. The dyslexic and comorbid groups had comparable working memory but dissimilar sentence quality. Conclusion: Contrary to literature-based predictions, phonological working memory and sentence production are weakly related in school-age children.