I agree. Some educators believe that children construct their own knowledge. They pick and choose what they assimilate. Before a child has reached the age of conservation, he cannot understand that concept. Even if we demonstrate to the young child that two differently shaped bottles contain the same amount of water, he will still believe that the taller bottle contains more water than the squat wide bottle. He will also believe that two halves of a cookie is twice as much cookie than the whole, unbroken cookie