Adolescents are more susceptible than adults to peer influence and to

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What This Claim Does NOT Say

Does not claim that peer presence compels conduct or removes responsibility for an individual's choices.

Does not claim adolescents are passively controlled by peers or cannot resist pressure at all.

Does not equate susceptibility to peer influence with a propensity for antisocial behavior — the two are measured separately.

Does not claim a specific age at which an individual becomes peer-resistant; maturation is gradual and varies between individuals.

Does not claim the effect is uniform across situations; it is strongest in arousing, peer-present contexts.

Scope — Where It Holds

A population-level developmental pattern. Susceptibility rises into mid-adolescence and declines as resistance to peer influence increases roughly linearly between ages 14 and 18, continuing to mature into the early twenties. Effects are strongest for spontaneous, emotionally arousing decisions made with peers present, and weaker for private, deliberate choices. Susceptibility to peer pressure is measured separately from willingness to engage in antisocial conduct, and describes group averages, not any individual.

Sources & Verification

Seminal

Gardner, M., & Steinberg, L (2005). Peer influence on risk taking, risk preference, and risky decision making in adolescence and adulthood: An experimental study. Developmental Psychology, 41(4), 625-635.
Experimental · N = 306 · 13-16, 18-22, 24+ (three groups)
Randomly assigning participants to perform tasks alone or with two same-aged peers, peer presence increased risk taking and reward-focused decisions among adolescents and youths but not adults.
Bearing on this claim: Randomized experiment: peer presence increases risk-taking in adolescents/youths but not adults.
doi.org/10.1037/0012-1649.41.4.625

Supporting

Steinberg, L., & Monahan, K. C (2007). Age differences in resistance to peer influence. Developmental Psychology, 43(6), 1531-1543.

Precedent Bridge

Relied on by

Roper v. Simmons (2005): "juveniles are more vulnerable or susceptible to negative influences and outside pressures, including peer pressure."543 U.S. 551 (2005)

Miller reaffirmed susceptibility to outside pressures as a mitigating feature of youth.567 U.S. 460 (2012)

Relevant to

J.D.B. v. North Carolina (2011) (quoting Roper and Eddings): children are "most susceptible to influence and outside pressures"; "a reasonable child subjected to police questioning will sometimes feel pressured to submit when a reasonable adult would feel free to go."564 U.S. 261 (2011)

Limits & Counter-considerations

Much evidence relies on laboratory tasks and simulated risk (e.g., a driving game) whose real-world generalization is debated; samples are largely U.S./Western; self-report resistance measures are susceptible to reporting bias; effect sizes vary; and group averages obscure substantial individual variation.

Adolescents are more susceptible than adults to peer influence and to external pressure or coercion, with susceptibility greatest in mid-adolescence; the mere presence of peers measurably increases adolescents' risk-taking and shifts their decisions toward immediate rewards.

For the Court