Prior studies with adults indicate that individuals with lower working memory capacity make less accurate metacognitive monitoring judgements and that within one individual, monitoring accuracy suffers when working memory demands increase. This is suggestive of a dependent relationship between metacognitive monitoring and working memory in adults. In the current study, we asked whether the same relationship is observed earlier in development, and whether the nature of this relationship is stable across middle childhood. An experimental approach was taken in which the working memory demands of a task were manipulated and the impact on children’s metacognitive monitoring accuracy was evaluated. The study had a mixed cross-sectional and longitudinal design, and the data indicate that children can also monitor their memory performance very effectively, with no developmental changes in relative monitoring accuracy. However, in contrast to the analogous adult data pattern, increased working memory demands did not lead to an impairment of monitoring accuracy in primary school-aged children. In fact, at the first assessment time point children showed higher monitoring accuracy when working memory demands were increased. This may reflect the qualitatively different processes involved in making monitoring judgements in childhood. It is anticipated that the results from the current study will provide novel insights into the nature of the relationship between working memory and metacognitive monitoring in development.