various levels of a child's environment. The primary focus of this theory focuses on the quality and context of a child's environment. Bronfenbrenner suggested that as a child grows older, their interaction between the various levels of their environment grows more complex due to cognitive abilities expanding. Lawrence Kohlberg wrote the theory of stages of moral development, which extended Piaget's findings of cognitive development and showed that they continue through the lifespan. Kohlberg's six stages follow Piaget's constructivist requirements in that those stages can not be skipped and it is very rare to regress in stages. Notable works: Moral Stages and Moralization: The Cognitive-Development Approach (1976) and Essays on Moral Development (1981) Jean Piaget Jean Piaget was the first psychologist and philosopher to brand this type of study as "cognitive development". Other researchers, in multiple disciplines, had studied development in children before, but Piaget is often credited as being the first one to make a systematic study of cognitive development and gave it its name. His main contribution is the stage theory of child cognitive development. He also published his observational studies of cognition in children, and created a series of simple tests to reveal different cognitive abilities in children. Piaget believed that people move through stages of development that allow them to think in new, more complex ways. Stages Sensorimotor stage The first stage in Piaget's stages of cognitive development is the sensorimotor stage. This stage lasts from birth to two years old. During this stage, behaviors lack a sense of thought and logic. Behaviors gradually move from acting upon inherited reflexes to interacting with the environment with a goal in mind and being able to represent the external world at the end. The sensorimotor stage has been broken down into six sub-stages that explain the gradual development of infants from birth to age 2. Once the child gains the ability to mentally represent reality, the child begins the transition to the preoperational stage of development. Each child is born with inherited reflexes that they use to gain knowledge and understanding about their environment. Examples of these reflexes include grasping and sucking. From 1 to 4 months of age, children repeat behaviors that happen unexpectedly because of their reflexes. For example, a child's finger comes in contact with the mouth and the child starts sucking on it. If the sensation is pleasurable to the child, then the child will