According to Erik Erikson's psychosocial stages, adolescents are faced with how they appear to others (especially same-age peers) and take this time to "try on" different roles to see how others react. This stage is completed when the individual has adopted a comprehensive identity. 

Lawrence Kohlberg developed three levels of morality to describe people: pre-conventional, conventional, and post-conventional thought. Pre-conventional thought is the most elementary of the three levels, in which actions are thought to be good or bad based on the rewards or punishments that stem from said action. 

Lawrence Kohlberg was the theorist who developed the concept that morality comes in three stages: pre-conventional, conventional, and post-conventional.

In the conventional stage of moral development, right vs. wrong is based upon societal conventions and expectations. Since Cody stated something that is a social convention, rather than a personal ethical belief, he is demonstrating features of the conventional stage of devlopment.

At stage three of Kohlberg's theory, which usually begins in adolescence or adulthood, people become conscious of how the society at large views their behavior. Thus, they are not necessarily concerned with gaining a direct reward or avoiding punishments, but rather focus on cultivating behaviors like appreciation and good manners that will make them well-liked by society. This stage is defined by conformity to societal expectations of behavior.  

Moral reasoning at the preconventional level focuses on punishment, rewards, and authority. The child in this question is exhibiting this degree of moral consideration.

Moral reasoning at the conventional level focuses on social order, upholding the law, and maintaining positive relationships. 

Moral reasoning at the postconventional level focuses on principles and values beyond laws that ensure individual rights. 

There is no unconventional level of moral reasoning, as presented by Kohlberg. 

Kohlberg's three stages are preconventional (in which morality is determined by the consequences for the person), conventional (in which morality is determined by social rules), and postconventional (in which morality is determined by core values). Since Elliott is choosing to keep the Earth clean not because he will get a fine or because his friends will judge him, but because of his own moral compass, this is an example of the postconventional stage. 

Lawrence Kohlberg is arguably the most influential psychologist in the field of moral development, particularly in children. He posits that humans can fall into three different stages of morality: preconventional, conventional, and postconventional morality. He used paradigms like the Heinz dilemma to assess children's responses, and determine which level of morality they possess. 

Also known as “identity crisis,” individuals in their late teens and early twenties struggle with discovering their identity. As these individuals begin venturing into the world, they struggle with who they are or want to be and their purpose in the world.

James Marcia proposed the Identity Status Theory based on Erikson’s stage of identity versus role confusion. His theory led to four different results: diffusion, foreclosure, moratorium, and achievement. Individuals drifting through life with no purpose or intention for exploration are in a state of diffusion. Individuals who have explored and discovered their purpose and identity are in a state of achievement. 

Piaget argued that children under the age of ten view the world in terms of Moral Realism, believing in fixed, universal rules and judging actions by their consequences, rather than the intent of the actor. After ten, he claimed, children learn that rules are socially created things that are adjusted as needed and begin to judge actions by the intent of their actors as they were done.