Adolescence is a period of substantial physical, emotional, and social development. Under the influence of puberty, adolescents’ bodies change, and so does the developing brain. Hormonal changes increase sensitivity to rewards and social feedback, while cognitive control systems continue to mature well into adulthood. As a result, adolescents become increasingly responsive to peers and social experiences. These biological and social dynamics create a developmental context in which peers play a central role and can provide both risks and opportunities. In this thesis, we examined how adolescents navigate social risks that arise in peer contexts. We focused on two complementary phenomena that reflect different ways in which adolescents’ social position can be affected: standing out and standing up. Standing out can increase vulnerability to rejection and exclusion, whereas standing up refers to taking risks to help others. The overarching aim of this thesis was to increase our understanding of how adolescents navigate social vulnerabilities and opportunities: when standing out makes them vulnerable, and what enables them to stand up for others despite risks. Standing out was examined in relation to off-time pubertal maturation and internalizing problems. Previous research typically assessed relative pubertal timing using population averages rather than adolescents’ direct peer environment. Therefore, we compared adolescents’ pubertal status to that of their same-sex classmates. Results showed that relatively early maturing girls reported more depressive symptoms, whereas no effects were found for boys. Relative pubertal timing was not associated with social anxiety, and comparing adolescents to their classmates did not provide additional explanatory value beyond absolute pubertal development. These findings suggest that adolescents’ social reference frames may extend beyond the classroom and that subjective perceptions of standing out may be more informative than objective comparisons. Standing up was studied through the lens of prosocial risk-taking, defined as behavior in which an individual takes a risk to help someone else. Because research on prosocial risk-taking is still emerging, the first step was to develop and validate a new measure: the Prosocial Adolescent Risk-taking Questionnaire (PAR-Q). The PAR-Q captures both social and material forms of prosocial risk-taking and showed good psychometric properties. Prosocial risk-taking was positively associated with empathy and prosocial behavior, and negatively associated with impulsivity and negative risk-taking. Subsequent studies used the PAR-Q to investigate factors underlying prosocial risk-taking. Building on existing theory, we examined the roles of empathy and sensation seeking. Across analyses, empathy emerged as the central factor underlying prosocial risk-taking, whereas sensation seeking played a more limited role than expected. Adolescents with high empathy reported the highest levels of prosocial risk-taking. In addition, communal social goals and donating to strangers emerged as relevant predictors. Together, these findings support existing theoretical distinctions while suggesting a refinement of models in which empathy plays a more central role. The final empirical chapter examined prosocial risk-taking in adolescents with ADHD. Although ADHD is often associated with increased negative risk-taking, little is known about positive forms of risk-taking. Adolescents with ADHD reported a higher likelihood of engaging in prosocial risk-taking than typically developing adolescents, providing an indication of the positive side of risk-taking in ADHD. Taken together, the findings of this thesis show how adolescents’ social worlds can simultaneously create vulnerabilities and opportunities. While standing out may increase the risk of social and emotional difficulties, standing up can motivate adolescents to take risks that benefit others. The results highlight the importance of considering not only the vulnerabilities of adolescence, but also its strengths. By examining both standing out and standing up, this thesis contributes to a deeper understanding of how adolescents navigate the social challenges and opportunities that characterize this developmental period.