tal line fixed at r). The opportunity cost is the
return from funds if they were invested for
purposes unrelated to disadvantaged children.
Conclusions
Investing in disadvantaged young children is a
rare public policy initiative that promotes fairness
and social justice and at the same time promotes
productivity in the economy and in society at
large. Early interventions tar geted toward
disadvantaged children have much higher returns
than later interventions such as reduced pupil-
teacher ratios, public job training, convict reha-
bilitation programs, tuition subsidies, or expend-
iture on police. At current levels of resources,
society overinvests in remedial skill investments
at later ages and underinvests in the early years.
Although investments in older disadvantaged
individuals realize relatively less return overall, such
investments are still clearly beneficial. Indeed, the
advantages gained from effective early inter-
ventions are sustained best when they are followed
by continued high-quality learning experiences. The
technology of skill formation shows that the returns
on school investment and postschool investment are
higher for persons with higher ability, where ability
is formed in the early years. Stated simply, early
investments must be followed by later investments
if maximum value is to be realized.
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10.1126/science.1128898
PERSPECTIVE
Studying Adolescence
Linda M. Richter
Young people in their teens constitute the largest age group in the world, in a special stage
recognized across the globe as the link in the life cycle between childhood and adulthood.
Longitudinal studies in both developed and developing countries and better measurements of
adolescent behavior are producing new insights. The physical and psychosocial changes that occur
during puberty make manifest generational and early-childhood risks to development, in the form
of individual differences in aspects such as growth, educational attainment, self-esteem, peer
influences, and closeness to family. They also anticipate threats to adult health and well-being.
Multidisciplinary approaches, especially links between the biological and the social sciences, as well
as studies of socioeconomic and cultural diversity and determinants of positive outcomes, are
needed to advance knowledge about this stage of development.
Y
oung people aged 10 to 19 currently
constitute a demographic bulge. They
are the largest age group in the world,
making up close to 20% of the 6.5 billion world
population estimated in 2005 (1), 85% of whom
live in developing countries and account for
about one-third of those countries_ national pop-
ulations. Adolescence has also been described as
Bdemographically dense[: a period in life during
which a large percentage of people experience a
large percentage of key life-course events (2).
These include leaving or completing school,
bearing a child, and becoming economically
productive. They also include experiences, more
common in this age group than in others, that
are capable of substantially altering life trajecto-
ries: nonconsensual sex, alcohol and drug abuse,
self-harm and interpersonal violence, and getting
into trouble with the law. Diet and activity pat-
terns, friendships, educational achievement, and
civic involvement all affect current health,
Child, Youth, Family, and Social Development, Human
Sciences Research Council, Private Bag X07, Dalbridge
4014, South Africa, and University of KwaZulu-Natal,
Table 1. Economic benefits and costs of the Perry
Preschool Program (27). All values are discounted at
3% and are in 2004 dollars. Earnings, Welfare, and
Crime refer to monetized value of adult outcomes
(higher earnings, savings in welfare, and reduced
costs of crime). K–12 refers to the savings in reme-
dial schooling. College/adult refers to tuition costs.
Perry Preschool
Child care $986
Earnings $40,537
K–12 $9184
College/adult $–782
Crime $94,065
Welfare $355
Abuse/neglect $0
Total benefits $144,345
Total costs $16,514
Net present value $127,831
Benefits-to-costs ratio 8.74
LIFE CYCLES
30 JUNE 2006 VOL 312 SCIENCE www.sciencemag.org
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