Lev S. Vygotsky developed a theory of cognitive development. He explained that experienced adults help children with innate basic capabilities to attain more complex and higher-order cognitive capabilities. To describe and assess this potential, he proposed the notion of ZPD. Based on Vygotskian thinking, an instructional process was developed in which the more knowledgeable partner adjusts the amount and type of support he offers to fit with the child's learning needs over the course of interaction. According to Vygotsky, psychological tools and signs facilitate and direct the thinking process.