The problems of adolescence are often blamed on the hormonal changes brought about during puberty, but recent discoveries in the study of brain development show that substantial maturation continues well beyond 18. We can't point to a specific chronological age at which the adolescent brain becomes an adult brain, because different brain regions mature along different timetables, but important developments are still ongoing during the early 20s. Treating adolescents as adults and setting adult expectations is misguided, at best. These years are the key period in determining individuals' life outcomes. How should we change the way we parent, educate, and understand young people?