ADOLESCENT DEVELOPMENT

Puberty occurs over an extended period of a young person's life during which developmental changes result in the maturation of primary and secondary sex characteristics and the acquisition of reproductive maturity. Pubertal development varies greatly from one individual to the next, and the age at which an adolescent matures depends on a combination of genetic and environmental influences, including early life experiences. Socially, pubertal maturation and its accompanying physical changes also affect how adolescents perceive themselves and how they are treated by others, and in this regard early pubertal timing has been shown to have challenging social consequences. Structural changes that disrupt the systemic factors that increase risk for early puberty (e.g., resource deprivation) as well as supportive relationships can mitigate the risks associated with early puberty and foster resilient outcomes.

Neurobiologically, throughout adolescence the connections within and between brain regions become stronger and more efficient, and unused connections are pruned away. Such developmental plasticity means adolescents' brains are adaptive; they become more specialized in response to environmental demands. The timing and location of these dynamic changes are also important. The onset of puberty brings about changes in the limbic region of the brain, resulting in greater sensitivity to rewards, threats, novelty, and peers. In contrast, it takes longer for the cortical region, which is implicated in cognitive control and self-regulation, to develop.

Consequently, adolescent brains are not simply “advanced” child brains or “immature” adult brains, but have evolved to meet the needs of this stage of life. Indeed, the temporal discrepancy in the specialization of and connections between brain regions makes adolescence unique. The developmental changes heighten sensitivity to rewards, willingness to take risks, and the salience of social status, propensities that are necessary for exploring new environments and building nonfamilial relationships. Adolescents must explore and take risks to build the cognitive, social, and emotional skills necessary for productivity in adulthood.

The increased cognitive abilities gained throughout adolescence also provide the capacity for other aspects of psychosocial development, such as developing identity and capacity for self-direction. An adolescent's identity is an emerging reflection of his or her values, beliefs, and aspirations, and it can be constructed and reconstructed over time and experience. Multiple factors, including family, culture, peers, and media, shape identity development, but young people are also active agents in the process. Ultimately, how adolescents' multifaceted identities are manifested—neurobiologically, behaviorally, or otherwise—and what role identity plays in their overall well-being greatly depends on their experiences in particular social contexts.

Adolescence is also marked by a growing capacity for self-direction. Over the course of adolescence, youth gain the cognitive skills needed to reflect on complex questions about their role in the world. This enables them to question the legitimacy and fairness of everyday experiences and of social institutions. Indeed, the social systems they must navigate—schools, employment, health care, justice—are complex, and navigating them often requires independent decision making. Such skills are important not only to support the transition to adulthood but also to make adolescence itself a period that fosters a propensity to contribute to others.

In summary, although adolescence is often thought of as a time of turmoil and risk for young people, it is more accurately viewed as a developmental period rich with opportunity for youth to learn and grow. Adolescence thus forms a critical bridge between childhood and adulthood and is a window of opportunity for positive, life-shaping development.

HOW ENVIRONMENT “GETS UNDER THE SKIN”: THE CONTINUOUS INTERPLAY BETWEEN BIOLOGY AND ENVIRONMENT

While the malleable brains of adolescents are adaptable to learning and innovation, they are also vulnerable to toxic exposures. The emerging science of epigenetics¹ focuses our attention on the ongoing plasticity of the brain and the reciprocal influences of the brain, body, and environment. Contrary to the common understanding that the effects of heredity are immutable and direct, contemporary studies of gene-environment interaction and epigenetics show that the way heredity is expressed in behavior depends significantly on environmental influences. The epigenetic approach also embraces a “trajectory” model of the life course: the trajectory of an individual's life may be changed, negatively or positively, at each life stage. Protective environmental factors support positive or flourishing trajectories, while adverse experiences may lead to at-risk or poor trajectories. The future condition of the brain and body will be affected by events that have changed the trajectory in the past, and interventions undertaken in the present have the potential to remediate past developmental challenges.

Adolescents' heightened sensitivity and responsiveness to environmental influences also implies “resilience,” meaning adolescents have the opportunity to develop neurobiological adaptations and behaviors that leave them better equipped to handle adversities that emerge throughout the life course. Thus, investments in programs and interventions that capitalize on brain plasticity during adolescence can promote beneficial changes in developmental trajectories for youth who may have faced adverse experiences earlier in life or are facing them now and prevent future challenges and risks.

INEQUITY AND ADOLESCENCE

The promise of adolescence can be severely curtailed by economic, social, and structural disadvantage and, in all too many cases, by racism, bias, and discrimination. These potent societal determinants shape adolescents' life-course trajectories in multiple ways, not only by reducing access to the opportunities, services, and supports enjoyed by more privileged youth but also by exposing less privileged youth to excess risks, stresses, and demands. These excess pressures “get under the skin” and adversely affect the brain and body during this critical developmental period.

Striking differences in opportunity are associated with striking differences in outcomes—in health, safety, well-being, and educational and occupational attainment—and in trajectories over the life course. Educational achievement, as measured by reading and math proficiency, high school graduation rates, and college completion, varies by race and ethnicity, socioeconomic status, and gender, with White and higher-income youth consistently experiencing better outcomes than other groups. Disparities also exist in the occurrence and impact of chronic health conditions (by socioeconomic status) and mortality (by race and ethnicity, socioeconomic status, and gender), due in part to exposure to violence. Moreover, there is consistent evidence that at all ages, LGBT youth are at higher risk of poor mental health and suicide than their heterosexual and cis-gender peers. Among adolescents, poor and Black youth are dramatically overrepresented in foster care. And in the juvenile justice system, Black youth are detained at a rate six times higher than White youth and three times higher than Latinx youth. (See Chapter 4.)

These disparities are often compounded for the youth experiencing them because they cut across the multiple systems with which they interact, and deficiencies in one area negatively affect outcomes in others. For example, poor health reduces educational attainment, while involvement in child protective services negatively affects juvenile justice outcomes. Together, these disparities grow as youth age and result in large disparities in their adult outcomes, such as poorer rates of employment and earnings, increased likelihood of criminal justice involvement, and poorer health and well-being.

However, disparities in adolescent outcomes are not immutable: they are responsive to changes in underlying conditions, and adolescents themselves show resilience and demonstrate strengths and assets that may be utilized to overcome inequities. Recent trends show that, in fact, adolescent well-being has improved over time, as illustrated by the steady decline in teen childbearing rates since 1990, which have been accompanied by significant declines in disparities by race and ethnicity.

Because a full understanding of the sources of these outcome disparities is necessary to formulate effective strategies for reducing them, we categorize the possible sources of these disparities as follows: (1) differences in family wealth and income, combined with living in neighborhoods segregated by income and race, (2) differences in institutional responses to adolescents by schools, the health system, the justice system, or the welfare system, and (3) prejudicial or discriminatory attitudes or behavior on the part of the adults or peers who interact with adolescents on a regular basis. Of course, other possible sources of outcome disparities exist, but here we point to some of the specific, quantifiable sources that have been captured empirically.

More than 9 million children and youth (ages 0 to 18) in the United States live in households with incomes below the poverty level, and rates of child poverty are highest for Black, Latinx, and American Indian and Alaska Native youth. For adolescents, growing up in poverty is associated with worse physical and mental health, as well as higher prevalence of risky behaviors and delinquency. The stagnation of wages for those in the bottom half of the income distribution over the past 50 years has reduced the resources available to lower-income families for investment in their children. Like income, wealth accumulation affects the resources families have available for investing in the next generation, especially for investments in higher education. Racial differences in wealth are three times greater than racial differences or gaps in income, with the average White household in 2010 having nearly six times the wealth of the average Black household (see Chapter 4).

In addition, because of the relatively high rates of residential segregation in the United States, adolescents from poor or minority families are much more likely than others to live in poor and segregated neighborhoods. Low-income neighborhoods, in turn, are more likely than other neighborhoods to be lacking in access to health care, youth-oriented organizations, and learning centers, and they are also more likely to be located near polluting factors, to have high levels of violence and low levels of safety, and to have low-quality housing. Moreover, poor families and minority families experience considerably more stress than others. As a result, not only are poor families less able to invest financially in their children, but also their nonfinancial investments, such as the amount and quality of their caregiving, are also affected by family disadvantage.

This disparity in family resources is often compounded by the institutions and systems with which youth interact. Segregation of schools by family income is the single most predictive factor of academic achievement gaps by race and income. The increasing income segregation of U.S. schools, compounded by rising income inequality, has most likely prevented society from achieving the full benefit of the significant, recent gains in financial parity across schools, suggesting that children from disadvantaged households likely need more resources (not equal resources) if society is to reduce disparities in educational outcomes. School segregation is driven largely by neighborhood segregation and, as such, the policy or institutional response to the increasing segregation of U.S. schools largely lies in housing policy, but tightness in the housing market and housing discrimination reduce the likelihood that low-income families can move to low-poverty neighborhoods. Moreover, lack of health care access and low health care quality, as well as laws and policies that drive crossover from involvement with the child welfare system into involvement in the juvenile justice system, compound disadvantage and contribute to disparities in opportunity.

A third source of disparities in adolescent outcomes derives from the explicit and implicit (or unconscious) prejudice and bias that individuals hold against groups defined by race, ethnicity, gender, LGBTQ identity, ability status, and so on. The experience of being targeted by such bias can include both singular significant interactions as well as a series of less obvious but frequent events, referred to as micro-aggressions. At a time when adolescents are especially sensitive to the attitudes and behaviors of adult members of the community, evidence suggests that educators, health professionals, child welfare system actors, and justice system actors exhibit behaviors that lead to disparate treatment of youth by race, gender, LGBTQ identity, and ability status. When aggregated in an institutional context, these biases can result in disparate outcomes for the affected groups.

An effective strategy, or set of strategies, to reduce inequities needs to address the main sources of these disparities. The committee recognizes some promising policies and programs that attempt to tackle these disparities in opportunity, including (1) policies and programs to reduce disparities in income, wealth, and neighborhood resources, such as the Supplemental Nutrition Assistance Program and the Earned Income Tax Credit; (2) trauma-informed approaches preparing adults serving youth to address differential exposure to violence and trauma among youth; and (3) emerging tools, such as predictive analytics, to erase or counteract bias in decision making by system-level actors.

With any strategy, greater coordination is needed across the multiple systems responsible for adolescents: the school system, health care system, and juvenile justice and child protection systems. Parity in public system funding is a first step, but it will not be sufficient to significantly reduce disparities. To significantly reduce or eliminate disparities, disadvantaged youth will likely require disproportionate funding.

Although progress may not be immediate, there is substantial reason for optimism. Progress has already been made in reducing disparities in adolescent outcomes, especially in the areas of education, health, and teen pregnancy. With the notable exception of the juvenile justice system, the evidence suggests that as overall adolescent health and well-being improve, disparities fall. These trends underscore the hope that with additional effort and a comprehensive approach, further reductions in outcome disparities among adolescents are indeed attainable.

USING DEVELOPMENTAL KNOWLEDGE TO ASSURE OPPORTUNITY FOR ALL YOUTH

The committee's charge requested recommendations regarding ways by which youth-serving systems—education, health, child welfare, and justice—can apply accelerating knowledge about adolescent development (and particularly knowledge from the neurobiological and socio-behavioral sciences) to their own work. Of course, investing in youth also requires investing in the adult caregivers who support them, as supportive familial, caregiver, and adult relationships play a significant role in fostering positive outcomes for adolescents. Such investments need to be multilevel and multisectoral; interventions to change parenting behavior may be futile if the systems themselves are not attuned to the pressing economic needs of parents.

The following sections briefly identify the major domains of the committee's recommendations for each of the four youth-serving systems designated in the committee's charge: education, health, child welfare, and justice. Detailed recommendations for specific actors and actions can be found in Chapters 6 through 9.

CONCLUSION

Adolescence, spanning the years from the onset of puberty to adulthood, is a formative period when changes in cognition, affect, and interpersonal behavior occur alongside the most extensive neurobiological transitions since infancy, especially with respect to pubertal and brain development. These changes make it clear that adolescent brains are not best understood as simply “advanced” child brains or “immature” adult brains. Instead they have evolved to meet the developmental needs of humans at this stage of life. Collectively, the pubertal, neurobiological, cognitive, and psychosocial changes occurring during adolescence mark this as a period of great opportunity for adolescents to flourish and thrive.

However, in the United States today many families lack adequate resources and neighborhood supports, leaving many adolescents at significant disadvantage during this critical period of development. To fail to address the sources of these disparities is to waste human capital: lower worker productivity, lost wages and employment, worse health and mental health, increased criminal justice involvement, and a drain on public support. These outcomes would reduce economic growth and exacerbate rising income inequality. Creating positive impact by improving opportunities for adolescents not only improves trajectories relevant to multiple outcomes, but also, by making use of high-impact, cost-effective interventions, it can counteract the effects of childhood stresses and deprivations and prevent negative outcomes in adulthood.

These realities also highlight a compelling scientific challenge. To understand how we can help all adolescents flourish, we need to connect two bodies of research: the deepened understanding of developmental processes needs to also encompass a richer understanding of the impact of the social environment. Achieving this will require a major commitment by our research establishment. Future research investments in adolescence should support efforts that (1) deepen our knowledge of the processes of adolescent development, (2) examine the socio-environmental contexts that offer opportunities for flourishing, and (3) understand and combat inequities that curtail the promise of adolescence for all youth.

Our society has a collective responsibility to build systems that support and promote positive adolescent development. These systems should reflect a rich understanding of the developmental needs of adolescents and a specific recognition of adolescence as a time of great opportunity to promote learning and discovery and to remediate past developmental challenges. Until society embraces this responsibility, the promise of adolescence will remain unfulfilled for millions of youth.