Background: Limited studies have been conducted on delineating the rationale behind individual differences in children developing metacognitive knowledge, as well as reading and writing proficiency. Aims: This study examined the dynamics of children's development of metacognitive knowledge as well as reading and writing proficiency during their progression from Grade 1 to Grade 6. Sample(s): A total of 420 students participated in the study, who were tested 6 times to assess their metacognitive knowledge, reading, and writing proficiency. Methods: The participants were invited to complete three tests--metacognitive knowledge, reading, and writing, which were administered at the end of each grade year. Results and conclusions: Three variables (i.e., metacognitive knowledge, reading, and writing) showed high stability and increasing variance over time. These findings suggest individual differences in children's development of metacognitive knowledge, as well as reading and writing proficiency. Students' metacognitive knowledge grew more quickly among those who entered primary school with already strong metacognitive skills; the same was true for their reading and writing development. Results also revealed predictive effects of students' metacognitive knowledge on their reading and writing performance. Implications are discussed based on these findings.