Conservation is one of Piaget’s developmental accomplishments, in which the child understands that changing the form of a substance or object does not change its amount, overall volume, or mass. This accomplishment occurs during the operational stage of development between ages 7 and 11. You can often see the lack of conservation in children when there are, for example, several different sizes of juice on a table, and they choose the glass that is the tallest because they perceive the taller glass as having more juice inside of it (even though the tallest glass may also be the thinnest). All the glasses may have the same amount of juice in them, but children who haven’t accomplished conservation will perceive the tall glass as being most full.