Inspired by the Supreme Court’s embrace of developmental science in a series of Eighth Amendment cases, “kids are different” has become the rallying cry, leading to dramatic reforms in our response to juvenile crime designed to eliminate the incarceration of children and support their successful transition to adulthood. The success of these reforms represents a promising start, but the “kids are different” approach is built upon two flaws in the Court’s developmental analysis that constrain the reach of its decisions and hide the true implications of a developmental approach. Both the text of the Court’s opinions and the developmental and neuroscientific research on which the opinions rely reveal that the developmental approach is not coherently defined by the legal line between childhood and adulthood. This lack of alignment has led to calls to extend the age of juvenile exceptionalism to young adulthood. But extending the exceptionalist frame obscures the central role that immaturity plays in most offenders’ full criminal careers and preserves a destructive fiction that youthful offenders are a distinctive, more sympathetic, and less corrupt subset of the millions of people charged with committing crimes. This Article argues that the developmental approach, followed to its logical conclusion, calls not for an age extension for juvenile exceptionalism but rather for a wholesale remaking of the entire criminal justice system in line with an abolitionist vision.