The Piagetian stage of cognitive development characterized by mastery of conservation tasks is the concrete operational stage. At this particular stage, the child has acquired all the proper skills to develop the seven conservation tasks. In the pre-operational period, children are likely to fail at mastering these tasks.
Conservation tasks are defined by the child´s ability to comprehend that something remain sthe same in quantity regardless of its appearance. An example of the conservation of mass task could involve Play-Doh; the child understands that if the Play-Doh is flattened, rounded or squared, it is the same amount. According to Simply Psychology, the concrete operational stage occurs between four and six years of age, far earlier than Piaget's original estimate of 7 to 11.