According to a new study, one in 4 Americans is a teenager or young adult, and the period represents some of the greatest peril and promise of their lives. Supports or inequities in adolescence are particularly likely to "get under the skin" of adolescents developing who they will be as adults. Emerging research identified adolescence and young adulthood—the period roughly from ages 10 to 24—as a second "critical window" of brain development after the early years. During this time, students become better at social learning, pattern recognition, and more responsive to changes in school and academic climates. Teenagers have been found to gain or lose as many as 20 IQ points during this period, making testing potentially less valid at the exact time it is used for critical decisions about their educational trajectory. Math or reading gender gaps can close or even flip. Teenagers' brain malleability, the research committee found, means that interventions during secondary school can help students overcome trauma or adversity in their early life. But adolescents also become increasingly aware of and damaged by bias, stereotypes, and institutional or social inequities, the report found, which can create "missed opportunities" for learning and becoming more resilient. Instructional interventions considered effective with younger students can suddenly backfire, and adolescents also have the greatest risk for developing mental illnesses or becoming involved in the justice system.