Conservation

They also typically lack conservation: understanding that an amount remains unchanged when its appearance changes, provided nothing is added or removed. For example, they may think that spreading a row of counters further apart creates more counters. Their judgement is influenced by the row's appearance rather than by the unchanged number.

These changes support conservation: understanding that quantity remains constant despite a change in appearance, as long as nothing is added or removed. After water is poured into a differently shaped glass, a child can reason that the amount is unchanged. Decentration allows them to consider both dimensions; reversibility allows them to imagine pouring the water back into the original glass.