How to move ArrayList with child class

Next, I have a ArrayList of type Student (which is an abstract class), and I have two child classes ( EstudanteGraduacao and EstudantePosGraduacao ), when I add them to ArrayList is quiet, but how do I go through it with an object of the daughters?
For example when I do:

for(Estudante e : estudantes){
    return e.getX();
    // considerando getX um metodo de Estudante
}

It works, the problem is that I do not know how to access the methods of EstudanteGraduacao ...

Anyway, I hope it was clear, I appreciate the help