Question
A four-year-old agrees that two identical short glasses hold the same amount of juice. An adult pours the juice from one glass into a taller, narrower glass while the child watches, and the child then says the taller glass has more juice. Which of the following best identifies the stage and the construct this response demonstrates?
- a.Sensorimotor stage; the child has not yet acquired object permanence
- b.Preoperational stage; the child is centering on one dimension and so fails to conserve
- c.Preoperational stage; the child is displaying egocentrism
- d.Concrete operational stage; the child has just acquired conservation
- e.Formal operational stage; the child is reasoning hypothetically about volume
Correct answer
B. Preoperational stage; the child is centering on one dimension and so fails to conserve
Full reasoning
- 1Fix the stage from the ability that is missing rather than from the age alone: the child cannot hold quantity constant across a change in appearance, which is a failure of conservation.
- 2Conservation is acquired in the concrete operational stage, so its absence places the child in the preoperational stage — consistent with the stated age of four.
- 3Name the mechanism precisely: the child attends to a single salient dimension, height, and ignores width, which is centration. Irreversibility of thought is the closely related limit that prevents her from mentally pouring the juice back.
- 4Rule out the same-stage distractor: egocentrism is a perspective-taking limitation, so it would be demonstrated by assuming another person sees what she sees, not by misjudging a quantity.
Why each choice is right or wrong
Choice A
Object permanence concerns whether a hidden object is understood to still exist, and it develops before age two. Nothing here is hidden, and a four-year-old using language this fluently is well past the sensorimotor stage.
Choice B
Correct. The child judges quantity from height alone and ignores the compensating decrease in width, and cannot mentally reverse the pour. That is centration, and the resulting conservation failure is the signature of preoperational thought.
Choice C
The stage is right but the construct is wrong. Egocentrism is difficulty taking another person's point of view, as in the three-mountains task; this child's error is about a physical quantity, not about someone else's perspective.
Choice D
This inverts the diagnostic. Passing conservation is what marks entry into the concrete operational stage, so a child who fails it has not yet reached that stage.
Choice E
Formal operational thought is abstract and hypothetico-deductive and does not appear until adolescence. The child here is not reasoning hypothetically at all; she is reporting what the glass looks like.
Related formula
Piagetian stage ladder
sensorimotor (0-2, object permanence) -> preoperational (2-7, egocentrism, centration, no conservation) -> concrete operational (7-11, reversible logic on concrete material) -> formal operational (11+, abstract and hypothetical reasoning)
Assumptions: Ages are textbook approximations; items test the order and the defining ability rather than the boundaries.
Related topic and practice
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Sources
Authored for this public explainer registry. It has no database question ID and is not copied from a protected or official exam bank.
- Psychology 2e, Section 9.2: Lifespan Theories — OpenStax. Accessed 2026-08-15. OpenStax textbook content is CC BY-NC-SA 4.0; attribute and avoid verbatim reuse beyond short cited references.
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