In 2012, the United States Supreme Court struck down existing legislative statutes mandating life without parole sentencing of convicted homicide offenders under age 18. The Court’s core rationale credited research on brain development that concludes that juveniles are biologically less capable of complex decision-making and impulse control, driven by external influences, and more likely to change. Closer scrutiny of the research cited in the defendants’ amicus brief; however, reveals it to be inherently flawed because it did not include relevant populations, such as violent offenders; utilized hypothetical scenarios or games to approximate decision-making; ignored research on recidivism risk; made untenable leaps in their interpretation of relevance to the study of homicide, and failed to include contradictory evidence, even from the brief’s authors. In forensic assessment, a blanket assumption of immaturity based on a homicide offender’s age is not appropriate, as research has demonstrated that in relevant respects, older adolescents can be just as mature as adults. An individualized and thorough assessment of each juvenile offender, including an analysis of personal history, behavioral evidence such as pre, during, and post crime behavior, and testing data more accurately inform questions of immaturity and prognosis in juvenile violent offenders.