he was of the first person in study the develope of the children. he separated the develope in stages of learnig. the firts estage is sensory motor, from the children was born to one o two years old. Next stage is preoterative from two to seven years old. The third stage is the stage of the specific operations from 7 to 11 years old. the last stage is the abstract thinking fron 12 years old to all the life.
their studies are, to this day, very important for the teachers of the school to distinguish the content of their classes, which are the best acording to their age,abilities according to their age.