Cady meets classmates who eventually become her friends, Janis and Damian. These two figures help show Cady around the high school, which helps Cady assimilate. The two show Cady the do's and don'ts she must follow to "survive" high school. These two are key figures because they helped mold her into how an American teenager should act during the early 2000s at a public high school. They also help her recognize in the end that true friendship is between the people who expect you for who you are rather than who you are trying to be.

While at North Shore High, Cady stumbles into another set of people who will become her "friends." These girls are called "the plastics". The group consists of Regina, Karen, and Gretchen. These girls befriend Cady one day and prompt her to follow a long set of rules to keep them as her friends. This ranges from only wearing pink on Wednesdays, only being allowed to wear sweatpants or jeans on Fridays, and maintaining a certain glam look and weight. They even pressure Cady to dress more promiscuous and engage in sexual activity.

Another vital component of Cady's microsystem is her math teacher, Ms. Norbury. When Ms. Cady transferred to North Shore High School, Ms. Norbury immediately liked her because Cady was bright and sweet and reminded her of herself when she was younger. Because she saw Cady's potential, she often encouraged her to pursue various academic opportunities to put herself out there. Ms. Norbury was the reason why Cady joined their math competition team.

All of these key relationships Cady has within her microsystem help shape her into the person she is as she tries to figure out who she is as she grows through adolescence. Sometimes, the molding is positive, and other times, the molding is more negative. Nonetheless, the molding occurs due to the intimacy of these relationships.

The stress of changing to new schools due to her parent's job is pivotal in her growth because it forced her into a new environment with people, which affected her academic performance.

The microsystem is the closest level to the child. The system involves intimate relationships that directly interact and effect the child. Examples would include a child's parents, siblings, teachers, or classmates.

Mesosystem:

The mesosystem is the second system focuses on how the various relationships in the microsystem work together which, in turn, effects the child. For example, if a child's parents have a good relationship with their teacher, this indirectly effects the child because the teacher is more likely to treat them in a kind manner and offer the child help with their school work would in turn effect their academic performance.

Exosystem:

The exosystem is the third system and gets a bit broader. During this level, things such as societal beliefs and structures effect the child's microsystem which, then effects the child. An example would be the government cutting educational funding at a child's school. This would then effect the quality of education a child will receive which will in turn effect the child.

Macrosystem:

The macrosystem deals with all of the cultural aspects that influence a child's development. These cultural aspects also include gender roles and social issues as well. For example, if a child grows up in a culture where women are expected to take care of the house instead of seek higher education, this will effect the child's development because it effects how they view education and can even effect their academic performance.

Chronosystem:

The chronosystem is the most broad level of the ecological systems theory and deals with the transitions that a child goes through over their lifetime. Examples would include major historical events such as a pandemic or growing up during the time of a major war.

Another critique of Bronfenbrenner's theory is that it is a theory that is extremely hard to test. Correlation does not always equal causation so there is no way to definitively tell if the systems that Bronfenbrenner has created are directly cause the effects that he claims they do.