Conservation of number is the understanding that the number of objects remains the same when they are rearranged spatially.  Piaget proposed that number conservation develops when the child reaches the stage of Concrete Operations at around 7 years of age.     Around this time, children also develop an understanding of other forms of conservation (e.g., weight, mass).  However, number conservation is often the first form of conservation to develop.  Before the stage of Concrete Operations, children may believe that the number of objects can increase or decrease when they are moved around.  Watch as this 5-year-old girl demonstrates that she does not yet understand conservation of number.  First she says that there are the same number of red chips and white chips in the two rows of chips made by the experimenter.  However, then she says that there are more white chips after the experimenter moves them farther apart in their row.