Conservation refers to a logical thinking ability which, according to the psychologistJean Piaget, is present in children during the preoperational stage of their development at ages 4-5, but develops in the concrete operational stage at ages 7-11. Conservation refers tothe ability to determine that a certain quantity will remain the same despite adjustment of the container, shape, or apparent size Irreversibility is a concept developed in this stage which is closely related to the ideas of concentration and conservation. Irreversibility refers to when children are unable to mentally reverse a sequence of events. In the same beaker situation, the child does not realizethat, if the sequence of events was reversed and the water from the tall beaker was poured back into its original beaker, then the same amount of water would exist.