Piaget describes four stages of cognitive development.
Simply stated Piaget stresses concept development before speech. Vygotsky urges the use of speech to develop concepts. Again, I don't believe it is an either or situation. Both aspects deserve our consideration and research suggests the child does both simultaneously.
Piaget describes four qualitatively different periods or stages of intellectual growth, which we pass through.
According to Piaget these stages can not be skipped, although some researchers disagree with this.
But Piaget does say that the time schedule for passing through the stages can be facilitated by experience.
Piaget also notes that there is no guarantee that an individual will pass through all of the stages. In most cases (not all) it takes formal instruction in high school and college to break into the highest stage.