English-speaking children sometimes make errors in production and comprehension of biclausal questions, known as “Scope-Marking Errors”. In production, these errors surface as medial wh questions (e.g., What do you think who the cat chased? (Thornton, 1990)). In comprehension, children respond to questions like How did the boy say what he caught? by answering what was caught (de Villiers & Roeper, 1995). These errors resemble wh-scope marking questions, attested in languages like German. Together, these errors suggest temporary adoption of multiple UG-licensed grammars (e.g., Yang, 2002). However, Lutken et al. (2020) found that children who make these errors in production do not necessarily make errors in comprehension and vice versa. They suggest these errors stem from children’s immature processing mechanisms. This article examines children’s production, comprehension, and processing capabilities, specifically working memory (WM). We find a correlation between WM and error rate and suggest separate causes for production and comprehension errors.