We used direct brain recordings in pediatric neurosurgical patients to understand how key memory regions interact during memory formation – a long-standing question in human neuroscience. Results reveal slow and fast theta oscillations, which separate across development and support distinct functional connections. Strengthened functional and structural connections differentiated top-performing adolescents from lower-performing adolescents and children. Findings suggest that the development of memory is rooted in the development of the brain’s ability to multitask. Paper published in Current Biology.