"…research on adolescent brain and behavioral development has provided additional support for Justice Kennedy’s observations. There is now a consensus among neuroscientists, for example, that brain regions and systems responsible for foresight, self-regulation, risk assessment and responsiveness to social influences continue to mature into young adulthood. This evidence that adolescents are psychologically and neurologically less mature than adults should be important in deciding how to punish their criminal acts.
…even psychological experts are unable to distinguish between the young person whose crime reflects transient immaturity and the rare juvenile offender who may deserve the harsh sentence of life without parole. If experts can’t reliably make this determination, then it seems unlikely that juries and judges would be able to do much better.”