#models.py
class Classes(models.Model):
        classcode = models.CharField(max_length=15)
        classname = models.TextField()
        students = models.ManyToManyField(User)

class Test(models.Model):
        classes = models.ForeignKey(Classes, on_delete=models.CASCADE)
        name = models.TextField(max_length=100)
        points = models.ManyToManyField(User, default=0)

#forms.py
class TestForm(forms.ModelForm):
    class Meta:
        model = Test
        fields = ('classes', 'name')

class Classes(models.Model):
    classcode = models.CharField(max_length=15)
    classname = models.TextField()
    students = models.ManyToManyField(User)

    def __str__(self):
        return "{0}: {1}".format(self.classcode, self.classname)