MacKenzie is an elementary student who has demonstrated the understanding that even though the levels of liquid in two glasses may appear different, they can still have the same amount depending on the size of the glass. She can also line up items from smallest to biggest. Which stage of Piaget's cognitive development is MacKenzie most likely in

The answer is the Concrete operational stage.

Explanation:

The concrete operational stage refers to the third stage concerning the theory of cognitive development developed by Piaget. This period is seen during middle childhood, around age 7 and it continues until age 11. The principal characteristic of this period is related to the development of logical thought.

Thinking is considered a very concrete process, and during this process  children's thinking becomes more logical and sophisticated. This stage is also important in the transition that can take place between earlier stages of development and the coming ones.    

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