“During the concrete operational stage a child’s thought begins to include concepts of time, space, and number. Categories and principles are used, and the child can think logically about concrete objects and situations.
“Another important development at this time is the ability to reverse thoughts and operations… Reversibility of thought allows a child in the concrete operations stage to recognize that if 4 * 2 = 8, then 2 * 4 does, too. Younger children must memorize each relationship separately…
“Children in this stage are beginning to use generalizations, but they still require specific examples [i.e., concrete examples] to grasp many ideas. Expect a degree of inconsistency in the child’s ability to apply concepts of time, space, quantity, and volume to new situations…