MR / Schenectady, NY.Photo 1 of a sequence of 3 .Boy (5, Nigerian-American & Ecuadorean-American) looks at juice in 8-ounce glasses of different heights..This sequence illustrates one aspect of Piaget's theory of cognitive development in the pre-operational child (aged approximately 2 - 7). One characateristic of the pre-operational child is the inability to conserve, that is understand that the amount of substance remains the same despite a change in shape/form. When the 8 ounces of juice in a short glass is poured into an 8-ounce taller glass, the child believes that the taller glass contains more juice than the shorter one..MR: AD-pkf Rab1..©Ellen B. Senisi