• by which new learning occurs (Piaget and Inhelder, 1969). Because people and their experiences are different, they arrive at school with varying levels of proficiency. A student is challenged according to his or her individual zone of proximal development (Vygotsky, 1986). The difference between a student's actual developmental level and his or her potential is the zone of proximal development (ZPD). Good instruction matches each child's ZPD.