A high school student begins to adopt the fashion and language of their close friends, which leads to a noticeable change in their behavior and academic performance. Which category best describes this phenomenon?

The situation described is a clear example of peer group influence, which refers to how individuals change their behavior, attitudes, or appearance based on the people they spend time with. In high school, students often look to their friends for guidance on what is cool or acceptable, leading them to adopt similar styles and ways of speaking. For instance, if a student hangs out with a group that values casual dress and slang, they might start dressing in a more relaxed way and using the same language, which can shift their personality. This change can also affect their academic performance, as they may prioritize fitting in with their friends over focusing on schoolwork. Overall, peer group influence shows how powerful friendships can be in shaping a person's choices and life path.