Final answer:
Children perform tasks more efficiently in middle childhood due to enhanced cognitive skills and physical developments that include improved agility and coordination.
Step-by-step explanation:
Children become able to perform tasks more efficiently during middle childhood in part because of improved cognitive skills. During this period, typically between the ages of 6 and 11, children's thought processes become more logical and organized when dealing with concrete information. They gain a better understanding of time concepts, allowing them to plan and work toward goals. Furthermore, physical development plays a role as children gain agility, balance, and muscle coordination, contributing to their increasing efficiency in both cognitive and motor tasks.