A 2006 cartoon in The New Yorker shows parents ordering their adolescent son to go to his room until his cerebral cortex matures. This nicely illustrates how we have come to think about adolescents.
Specifically, the cartoon illustrates at least five assumptions about adolescents and their brains: (1) adolescents are categorically different from adults; (2) adolescents are less rational than adults; (3) adolescent cognition and behavior are explained by their teenage brains; (4) adolescent brain development is a maturational process directed by genes; and (5) the outcome of that process is a state of maturity achieved in adulthood.
All of these assumptions are false. Let me be clear: I am not just saying we do not have sufficient evidence to support some of these claims. I am saying we have plenty of evidence with regard to all of them, and the evidence shows them all to be false. For a detailed review, see my Adolescent Rationality and Development (3rd edition, 2011). For the short version, read on:
First, adolescents are indeed a distinct group with respect to children, but not with respect to adults. Even among young teens we commonly see forms and levels of knowledge and reasoning that are rarely seen in children under the age of 10 or 11. Development beyond childhood, however, is highly variable in direction and extent. There are, to my knowledge, no forms or levels of knowledge, reasoning or psychological functioning that are common in adults but rare among adolescents.
Second, research in cognitive psychology since the 1970s shows that we are all irrational much of the time. Adolescents are specifically accused of egocentrism, impulsivity, risk taking, peer conformity and inadequate future orientation. They are guilty as charged, of course, but adults of all ages fall short in all the same ways. Individual differences beyond age 12 to 14 are not strongly related to age. Many 14-year-olds function beyond the level of many 40-year-olds.
Third, we are very far from reducing psychology to biology, if indeed this can be done. We cannot predict or understand how adolescents perceive, infer, think, feel, act, reason or reflect by examining their brains. Our rich knowledge of adolescent functioning is the result of decades of psychological research on their cognition and behavior. Brain research is crucial for a full picture, but it does not provide an ultimate explanation.
Fourth, genes do not cause brain development. Genes are the outcome of evolution and the origin of a developmental process. The brain, however, is part of a dynamic system that includes an active organism interacting with an active environment. Its development is intricately intertwined with the development of that system. Brain development is as much the result of cognitive activity as its cause.
Finally, we adults are enthralled by mythic conceptions of a maturity we have attained that adolescents have yet to reach. We're right to think that we are more mature than children. But adolescents are also more mature than children, and not so different from us with respect to their brains, cognition and behavior.
Claims about the relative size and merit of the brains of various sorts of people have long provided a pseudoscientific basis for oppression of women, racial minorities and others with brains deemed inferior. The case against teen brains is no stronger.
Cognitive development often continues long beyond childhood, especially in cognitively rich and challenging environments that encourage active engagement and reflection. There is nothing about teen brains, however, to justify distinguishing adolescents from adults.
As for the adolescent in the cartoon, I don't know what he did or what his parents should do. Whatever the problem, however, waiting for his brain to grow up is surely not the solution.