The results of four experiments with 257 children from six to fourteen years of age carried out at school and in laboratory, enable us to arrive at the following conclusions:
1. The development with growing age of the pupils' ability to differentiate and form ideas proceeds according to the law of development by stages: the stages of relative calm alternate with periods of violent rise (»leaps of developnient «). The individual stages correspond to the Soviet classification of schoolage periods.
2. The differentiation ability is not changed by education. On the other hand, education greatly influences the formation of conditioned-reflex habits, skills and knowledge, which may »screen« or even »change to the contrary« the inborn Ways of the child’s response.
3. The ascertainment of two completely different types of differentiation confirms the existence of marked individual differences which education must take into account in the same way as the differences of age.