What law was used in the decision of Goss v. Lopez?

The Supreme Court case of Goss v. Lopez relied on the Due Process Clause of the Fourteenth Amendment. The Due Process Clause of the Fourteenth Amendment requires states to provide reasonable hearings and other legal procedures before depriving any person of life, liberty, or property.
The case involved nine students who were suspended from an Ohio high school for ten days without a hearing, meaning they were not able to defend themselves against the accusations that they destroyed school property and disrupted school.
Ohio law made education in the state a fundamental right by providing it, free of charge, to all Ohio residents between the ages of five and twenty-one. This made the students entitled to school and constituted a property interest that implicated the Due Process Clause. Therefore, the school’s decision to kick the students out of class for ten days could only be done if there was a hearing involved. According to the Supreme Court:

Having chosen to extend the right to an education . . . Ohio may not withdraw that right on grounds of misconduct, absent fundamentally fair procedures to determine whether the misconduct has occurred.