The Conservation Task

The conservation task is the single most iconic demonstration in Piaget's experimental repertoire. Two identical glasses hold equal water; the child agrees the amounts are equal. The experimenter pours one into a taller, thinner glass; the water level rises. 'Is the amount the same?' The preoperational child says no — the tall glass has more because the water is higher. The concrete operational child says yes — nothing was added, nothing removed. The task reveals, with diagnostic precision, the qualitative difference between two stages of cognitive architecture. It is also Piaget's canonical demonstration of productive disequilibrium: the transitional child who senses the conservation answer without being able to construct it is doing the most important cognitive work of her day.