This report has been inspired by important and exciting advances in the science of adolescent development that have been achieved in the 21st century, and the committee has no doubt that the scientific findings summarized in this report provide a firm foundation for resolute action by governments at all levels and by all stakeholders committed to the well-being of adolescents. However, for each advance, new questions and scientific opportunities arise. Although this report is focused on the implications and applications of current knowledge for changes in policy and practice, it is well to take note of some key priorities for future research as well as the limitations in existing data that will need to be addressed to move the field forward.
Until the early years of the 21st century, leading scholars of adolescence subscribed to the view that by adolescence the brain had developed all of the functional capacity that it has in adulthood. It was believed that life experience was the primary distinction between adolescents and adults with respect to a host of human functions and behaviors—including domains such as self-regulation, cognitive judgment, and decision making. The emergence of developmental neuroscience has profoundly challenged that idea, pointing instead to ongoing fundamental changes in the adolescent brain—changes that continue beyond the teenage years and into the mid-twenties. Thus, one of the biggest shifts in scientific thinking about adolescence during the 21st century has been a recognition that fundamental neurobiological mechanisms, involving their connections with each brain domain as well as with the environment, continue to develop.
Moreover, our ability to measure and understand these neurobiological processes in adolescents, and in humans generally, has grown at a remarkable pace, undergirded by advances in magnetic resonance imaging (MRI) scanning tools and techniques for processing and analyzing genetic material. Along with these technical advances has come a wave of research using these new methods and a proliferation of data and new knowledge.
We now understand that brain development does not end in early childhood, and it is never “too late” to change the trajectory of development. The adolescent brain is plastic and resilient. Compensatory mechanisms of recovery can often redirect development and change the trajectories of brain circuits and body systems. In short, our understanding of adolescence has grown by leaps and bounds, and the application of this knowledge has the potential to change developmental trajectories of adolescents who might otherwise have been left behind.
To capitalize on these gains in knowledge from neuroscience, it is critical to better integrate our understanding of adolescent development within a model that also incorporates the social-contextual influences experienced by contemporary youth, and particularly the challenges faced by disadvantaged youth, including the effects of growing up in an impoverished and dangerous neighborhood and the impact of bias and discrimination. Now is the time to pursue this work because of the surging public interest in brain development and the potential to guide the next generation of research on adolescent social and behavioral development. In sum, future research must embed neurobiology within a social-contextual framework that is inclusive and representative of today’s youth.
Although our knowledge about adolescence is growing rapidly, considerable gaps remain in pertinent data bearing on adolescent outcomes across sectors. Regarding health outcomes, for example, a 2007 review lamented the scarcity of data regarding specific health status or health objectives (e.g., increase the proportion of adolescents who engage in regular physical activity) for different adolescent populations, and recommended a “national adolescent data-priority agenda to develop strategies for improving health data regarding adolescent sub-populations” (Knopf et al., 2007, p. 335). This data gap has important implications for both researchers and policy makers, because inadequate outcome measures hamper our ability to design effective policies to address disparities. Below we discuss multiple reasons why measuring and assessing disparities in adolescent development is challenging, and why consideration of new methods and processes to overcome these limitations are needed.
First, a substantial proportion of the current developmental research categorizes adolescent subjects in fairly gross ways (for example, by gender and race/ethnicity but not by nativity or sexual orientation) and rarely allows analyses of intersections among groups. This makes it difficult to examine comparable measures across multiple groups of adolescents.
Second, studies typically aim to measure different outcomes at different points in time, thereby precluding a comprehensive profile of youth at a particular point in time. In addition, even if the data source collects information on a diverse set of variables, the sample may be incomplete; for example, many adolescent surveys (e.g., the Centers for Disease Control and Prevention’s (CDC’s) Youth Risk Behavior Survey or YRBS) are limited to school-enrolled adolescents, thereby leaving out many at-risk adolescents who have already left school. Further, the CDC’s work depends on partnerships with state school districts to collect these data, leading to variation in the modules included in the survey. For example, a state might be hesitant to collect data on issues pertaining to reproductive health and may only selectively collect data on other topics that are perceived to be less controversial in nature.
Third, even when more comprehensive data are available, the surveys tend to focus on problem behaviors, rather than indicators of positive youth development. For example, documenting declining rates in smoking tells little about the assets and strengths of young people.
Fourth, differences in the wording of survey questions among national sources of data (such as the National Health Survey, YRBS, and Medical Expenditure Panel Survey) may result in different profiles of the health status of youth depending upon the data source—for example, whether the adolescent or a parent completes the survey—or depending on the site of data collection (e.g., at school, at home, in a health care setting, at a youth detention center).
Fifth, because some groups of adolescents, including Native Americans, comprise a relatively small share of the population, a general population-wide survey is insufficient to measure their outcomes accurately. In some cases, as with respect to sexual orientation and gender identity, researchers may fail to collect information on these characteristics altogether, and some youth may be uncomfortable or feel unsafe disclosing this information.
Sixth, some adolescent outcomes that researchers believe to be important in terms of influencing adult outcomes are not easily collected. For example, while academic test scores of adolescents are widely available and relatively straightforward to collect, consistently collected measures of adolescent emotional well-being or conduct, both of which have been found to be highly predictive of future adult circumstances, are not (Layard et al., 2014).
Seventh, national datasets currently do not collect information on the perceptions and experiences of young adolescents regarding equity, disparities, and racism.
The previous chapters show that our understanding of adolescence has grown markedly in recent years. Advances in neuroscience coupled with deepening knowledge from the social and behavioral sciences have solidified our understanding of adolescence as a period of opportunity. But, as noted in Chapter 4, we also know that many youth are hindered in their development by persistent and worsening inequities in many domains, including family income and wealth and neighborhood resources. To harness the promise of adolescence, our nation will need to grapple with these two underlying realities: This critical period of life is ripe with opportunity for learning, growth, and development, which can be utilized not only to launch extraordinary career trajectories but also to remediate previous developmental setbacks during childhood. Yet persistent inequities in social and environmental conditions curtail opportunity for many adolescents.
These realities amount to a compelling scientific challenge as well as a political one. To understand how we can help all adolescents flourish, we need to connect these two bodies of research—deepened understanding of developmental processes must also encompass a richer understanding of the impact of the social environment. This will require a major commitment by our research establishment. Sketching out a research portfolio was not one of the committee’s core assignments (we were asked only to offer a handful of research recommendations), but we think it well within our charge to comment on the need to undertake a major investment in connecting developmental research on adolescence with the burgeoning research on social equity. This short chapter will set forth a few broad suggestions.
In undertaking this research effort, it is important to recognize that adolescents themselves have the capacity to make meaningful contributions to the design and execution of research. Future research funding can invest in youth expertise and agency by engaging youth in the research process. If we aim to use research to improve the conditions of youth’s lives, we must support opportunities to involve youth in identifying the issues that are most pressing for them and provide them with the skills to investigate those issues. An existing example of this is Youth Participatory Action Research (YPAR), an approach that empowers youth by equipping them with skills to systematically study issues in their communities (Cammarota and Fine, 2008; Ozer, 2016). Inherent in this approach is a belief in the capability of youth to rigorously investigate social challenges and take action to address
them (Berg et al., 2009). YPAR exploits the developmental opportunities afforded during adolescence (e.g., cognitive flexibility, openness to exploration) in order to create mutually beneficial change for youth and for society. Funding to support YPAR work is essential for advancing our knowledge of adolescent development in a manner that includes adolescents as critical stakeholders.
Moreover, to effect change, evidence must be translated into policy and practice. To this end, implementation studies should identify factors that can contribute to or impede effective and timely uptake and replication of adolescent research. Using implementation methodology, investigations should also examine system capacity for replicating evidence-based practices by, for example, identifying training needs of professional staff and community members and providing adequate reimbursement, and other system incentives to ensure replication of evidence-based practices with fidelity.
Future research investments in adolescence should support efforts that: (1) deepen our knowledge of the processes of adolescent development and the effectiveness of interventions, (2) examine the socio-environmental contexts that offer opportunities for flourishing, and (3) seek to understand and combat inequities that curtail the promise of adolescence for all youth.
Deepen Understanding of Developmental Processes and the Effectiveness of Interventions
Research seeking to deepen our understanding of the developmental processes of adolescence should consider the timing, type, and effectiveness of interventions for adolescents. These are the key questions: Given the rapid development of areas of the brain responsible for planning and decision making during adolescence, do interventions that rely on cognitive control (e.g., cognitive behavioral therapy) vary in effectiveness across the span of adolescence? Are there more effective windows within adolescence to deliver such interventions, where the adolescent brain is “ready” to benefit from the intervention? Do the most effective types of interventions therefore vary across adolescence? Is brain development a better indicator than chronological age of readiness as to when an adolescent can optimize the benefit from specific educational curricula?
Of course, in answering these questions it will be necessary to understand nature and correlates of individual variation in adolescent behavior and development, as age is an imprecise measure and brain maturation varies as much across ages as it does within ages (Galván, 2014). Current policy discussions applying the science of adolescence (using psychological and behavioral measures as well as neurobiological ones) have largely been based on group data due to methodological constraints necessitating inference based on a large sample of research participants. However, advances
in policy and practice necessitate greater understanding of whether generic guidelines about maturation can be established. A key question, as posed by Galván (2014, p. 264) is “whether individual variation [is] so great as to. preclude the establishment of a biological benchmark for adult-like maturity and judgment.”
Future research funding should also support
- studies that enact holistic approaches to understanding adolescent outcomes characterized by the consideration of achievement, health, and other outcome domains simultaneously;
- studies that demonstrate the specific social conditions and supports linked to epigenetic mechanisms that activate processes related to resilience and positive outcomes for young people, despite challenging circumstances;
- studies that identify, substantiate, and implement interventions that build locus of control and agency in adolescents and that promote resilience, for example by delivering specified curricula to youth and their caregivers, as was done in the Strong African American Families study (see Brody et al., 2017); and
- studies specifically designed to test optimal timing of interventions, posing questions such as “What are the trajectories of true developmental change in connectivity within and between neural networks implicated in cognitive control and emotional processing? Are these trajectories of change steeper or quicker during some periods than others potentially providing key windows for input and intervention?” (Fuligni et al., 2018, p. 151).
Examine Socio-Environmental Contexts
A large and rigorous knowledge base from developmental and intervention studies shows that adolescents (including both their brains and their behaviors) are influenced by their context, including their families, peers, schools, neighborhoods, and socio-cultural systems. Yet these influences on adolescent development have been neglected or obscured in much of the neurobiological research on adolescents to date, possibly because we lack good measures for assessing context—especially through the lenses of young people themselves. It is critical that future research better integrate our understanding of adolescent development within a model that incorporates social contexts and environmental influences experienced by today’s youth.
Important considerations in this context are whether adolescents (and their developing brains) are more sensitive to some features of the social environment than others and whether some adolescents may flourish in particular contexts while others may struggle in that same context
(Fuligni et al., 2018). The role of technology and digital media as a context for development provides one example of an area ripe for further exploration along these lines. Research in this area is burgeoning, but critics of this work have raised serious concerns about the quality of the evidence base. If it is the case that some adolescents are adversely affected by exposure to digital technology and media, it appears that others are unaffected, and still others benefit from it. A high priority for research is identifying characteristics of youth who are most at risk for deleterious consequences, as well as practices that moderate the potential outcomes (George and Odgers, 2015; Orben and Przybylski, 2019; Seabrook et al., 2016; Twenge et al., 2019).
Understanding how the social and environmental context (and factors within that context) can offer opportunities for flourishing outcomes or for worsened outcomes for youth and emerging adults is critical. Studies should focus on:
- Understanding the policy impact of laws and policies that improve or impede adolescent health, well-being, safety, and security;
- Ascertaining what social and economic policies may improve opportunities for youth to thrive and test whether their effectiveness differs by race/ethnicity or context; and
- Identifying what interventions might ameliorate and (or) enrich the outcomes of youth who have experienced childhood deprivation, oppression, or other negative experiences (such as poverty, trauma, separation, or displacement).
In conducting investigations of this type, it is also important to consider the need to replicate effects behaviorally. For example, if a specific brain region or channel of connectivity between brain systems is discovered through a lab-based functional MRI study, before researchers move to assess intervention implications it is important that their next step be to replicate these effects behaviorally in the youths’ social context. In other words, just because a brain pathway appears to light up when doing a task in a scanner, this does not prove that the same pathway will light up in the real everyday world, when peers, family, and other contextual factors are present.
Understand and Reduce Inequity
Understanding—as well as reducing—inequalities in the lives of adolescents is critical to ensuring that all adolescents have the opportunity to flourish. Our growing knowledge about disparities in adolescent outcomes, and the sources of those disparities, has the potential to inform the development of policies and practices designed to achieve equity and help all ado-
lescents flourish and thrive. This goal should be fundamental for all future research on adolescence.
In conducting this research, issues of inclusion and exclusion will be particularly salient. Much of the recent knowledge on adolescents—specifically that derived from MRI studies—has not been representative of contemporary youth. Individuals included in MRI studies have historically been individuals participating in federally sponsored research, often through a university medical facility. As a result, most of these studies have not been fully representative of individuals living in poverty, including ethnically diverse participants, those without medical providers, and those from rural areas. In order to better understand and combat inequities, future research endeavors will need to make efforts to remedy this bias through, for example, direct recruitment efforts and outreach to underrepresented communities.
Future research on adolescence should prioritize studies addressing:
- discrimination and marginalization, with a focus on both neurobiological consequences as well as structural strategies (school, community, state policies and practices) that reduce the conditions in which discrimination and marginalization are prevalent, and that buffer individuals from such experiences;
- youth who historically have been underrepresented, or who are most vulnerable (e.g., youth of color; immigrants; sexual and gender minorities; religious minorities; out-of-home youth or those experiencing homelessness, foster care, or unstable housing); and
- ways in which intersecting axes of oppression shape youth development, particularly against a backdrop of social stratification and oppression, where relationships between identity, experience, and behavior may not operate the same way for all youth.
Our new understanding of adolescence implies that the adolescent infrastructure should encompass basic and applied research aiming to inform policies and practices that nurture positive development for all children and youth from birth to adulthood. The changes in the brain, body, and behavior that occur during adolescence mark this as a distinct developmental period during which adolescents make critical advances in learning, development, and maturation, but are also susceptible to risk. Interventions made during this period hold promise for supporting positive developmental trajectories and remediating past developmental challenges and have the potential to prevent negative trajectories. Investments in this period, thus,
can support all adolescents to achieve flourishing trajectories and arrive at adulthood ready to thrive.
Creating positive impact through opportunities not only improves trajectories relevant to multiple outcomes, but also can provide high-impact cost-effective prevention of the elevated risk for negative trajectories during this period (Dahl et al., 2018). Thus, return on investment is not only the measurable positive impact of interventions, but also the savings from preventing later negative impacts that are costly in human as well as economic terms. For example, improving developmental trajectories in early adolescence (e.g., through health, education, and social development) can be an effective strategy for preventing many of the behavioral and emotional health problems that typically emerge in late adolescence—including the increasing rate of substance use, depression, anxiety, suicide, and school failure.
Much like precision medicine or the precision education contemplated in earlier chapters, investments can be targeted to maximize benefits for those most in need. As knowledge of adolescent development continues to increase, it will “lead to greater precision in understanding developmental risk factors and identifying the timing, mechanistic targets, and best contexts to improve adolescent trajectories” (Dahl et al., 2018, p. 447). Recent developmental neuroscience findings, for instance, suggest fundamentally different maturation processes may underlie the dysregulation that precedes anxiety and psychotic spectrum disorders (Tromp et al., 2019; Jalbrzikowski et al., 2019; Meyer and Lee, 2019). Such knowledge—including understanding how factors such as sex, genetic differences, early life adversity, and environment and context influence development—can be used to match interventions to specific developmental stages of adolescence, ultimately optimizing the value of the investment.
Marked increases in our understanding of adolescence has the potential to help all adolescents flourish. Yet, data limitations hamper our ability to understand adolescent outcomes across sectors. To benefit from recent gains in scientific understanding, these gaps will need to be addressed in combination with efforts that deepen our understanding of adolescent development, the socio-environmental contexts in which young people live, and the inequities that hinder opportunity for all adolescents.
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