Piaget
nSensory-motor
nPre Operational
nConcrete Operational (7-11 years). Characterized by 7 types of conservation: number, length, liquid, mass, weight, area, volume. Intelligence is demonstrated through logical and systematic manipulation of symbols related to concrete objects. Operational thinking develops (mental actions that are reversible).
nFormal Operational Intelligence is demonstrated through
the logical use of symbols related to abstract concepts. Only 35% of high school graduates in industrialized countries attain formal operational thought; many people do not think formally during adulthood