Final answer:
The single most important Supreme Court case with respect to juvenile justice is In re Gault, which established the constitutional rights of juveniles in delinquency proceedings.
Step-by-step explanation:
The single most important Supreme Court case with respect to juvenile justice is In re Gault, which was decided in 1967. In this case, the Court held that juveniles are entitled to due process protections, including the right to notice of charges, the right to counsel, the right to confront and cross-examine witnesses, and the privilege against self-incrimination. Prior to this decision, juveniles did not have the same constitutional rights as adults when facing delinquency proceedings. The decision in In re Gault significantly expanded the legal rights of juveniles and set the foundation for the development of the modern juvenile justice system.