Despite substantial improvements to memory precision in childhood, the neural mechanisms underlying these changes remain unclear. Here, 40 children (7-9 years; 22 females, 18 males; majority White) and 42 adults (24-35 years; 22 females, 20 males; majority White) modulated their approaches to memory formation--focusing on the specific details to encourage precision or general category to encourage imprecision. Children and adults alike formed more precise memories under the specific task, yet adults' neural states were more cohesive as a group than were children's. Moreover, children's adoption of an adult-like neural approach explained age-related gains in memory precision ([beta] = 0.08). Development unfolds as children--initially varying in their memory control--eventually adopt an adult-like approach that benefits memory precision around age 9.