Reading comprehension and writing are essential skills for success in modern societies. Additionally, reading and writing have been described as highly reflective activities that necessitate metacognitive monitoring and control. However, reading comprehension and writing are skills moderated by many factors, proficiency among them. Thus, in the present study we examined the influence of reading comprehension proficiency (proficient, poor) on elementary school students' (N = 120) metacognitive monitoring accuracy in reading and writing tasks. Further, we investigated the predictive patterns of linguistic indices between proficient and poor readers on their metacognitive monitoring accuracy in a writing task. Findings revealed that proficient readers exhibited significantly better monitoring accuracy in both reading and writing tasks, and that unique predictive patterns of linguistic indices on writing skill monitoring accuracy emerged between proficient and poor readers. We discuss the implications of these findings for research, theory, and practice and propose recommendations for future research.