Ognitive development and limitations of preschool children

Should the learning emphasis of kids aged 3-5 be placed on academic work or on improving social skills and self esteem? What aspects of the preoperational period of Piagets cognitive theory support your stance? How do the cognitive skills of conservation, egocentrisim, seriation, class inclusion and other mental attributes contribute to you position? How might our knowlege of congnitive skills as proposed by Piaget serve to help us understand what we should appropriately expect from our preschoolers?