Final answer:
In 2012, Stevenson and the EJI successfully won a constitutional ban on mandatory life-without-parole sentences for children convicted of homicides. This ban was established through the Supreme Court case Miller v. Alabama. Graham v. Florida also played a role in prohibiting life imprisonment without parole for juvenile non-homicide offenders.
Step-by-step explanation:
In 2012, Stevenson and the EJI (Equal Justice Initiative) won a constitutional ban on mandatory life-without-parole sentences imposed on children convicted of homicides through the Supreme Court case Miller v. Alabama. This case ruled that a sentence of life imprisonment without the possibility of parole may not be a mandatory sentence for juvenile offenders. Additionally, in 2010, the Supreme Court case Graham v. Florida also prohibited the imposition of life imprisonment without parole on juvenile non-homicide offenders.