Intelligence is significantly related to core cognitive abilities such as executive function and working memory. Mental attentional capacity is considered as the maturational component of working memory and corresponds to the amount of information that a person can simultaneously hold and process. Functional neuroimaging studies with adults show that prefrontal and parietal regions underlie function mental attention. Critically little is known about the brain correlates of mental attentional capacity in children. Functional magnetic resonance imaging examined the brain correlates of 18 children (9-12 years). Results show a linear relation in frontoparietal brain regions. Understanding neurobiological mechanisms underlying development of mental attentional capacity can inform educational practices and improve personalized teaching for children.