As briefly discussed in chapter 1, Vygotsky (1978, 1934/1986) viewed school instruction as the major avenue for mediated learning and, therefore, as the major contributor to children's cognitive development during the period of middle childhood. According to Vygotsky (1978, 1934/1986), the major reason for the development-generating effect of school instruction relates to students' acquisition of so-called scientific concepts, which can be contrasted with the spontaneous concepts of preschoolers.

Spontaneous concepts are the result of generalization and internalization of everyday personal experience in the absence of systematic instruction. Therefore, such concepts are unsystematic, empirical, not conscious, and often wrong. For example, a 3-year-old child, having observed a needle, a pin, and a coin sinking in water, comes to the wrong conclusion – that “all small objects sink” – and begins to use this concept for predicting the behavior of different objects in water (Zaporozhets, 1986c, p. 207). Despite their “unscientific” nature, spontaneous concepts play an important role in children's learning as a foundation for the acquisition of scientific concepts. For example, “historical concepts can begin to develop only when the child's everyday [spontaneous] concept of the past is sufficiently differentiated” (Vygotsky, 1934/1986, p. 194).

In contrast to spontaneous concepts, scientific concepts represent the generalization of the experience of humankind that is fixed in science (understood in the broadest sense of the term to include both natural and social sciences as well as the humanities), and they are acquired by students consciously and according to a certain system.