Trouble with binding source and combo boxes in C#

           // There are two classes.
            public class SchoolClass
            {
                   public string ClassName {get;set;}
                   public int Id { get; set;}
                   public BindingList<Student> Students {get;set;}
            }

            public class Student
            {
                    public string Name {get;set;}
                    public int Id { get; set;}
            }

            public class Report
            {
                       int MyClass;
                       int MyStudent;
            }

            // Get a collection of school classes, and report.
            BindList<SchoolClass> classes = GetClasses();
            Report report = GetReport();

            // Create a binding source to bind to binding list.
            BindingSource bsClasses = new BindingSource();
            bsClasses.DataSource = classes;

          // Set up the binding for my two combo boxes.
            cbClass.DataBindings.Add("SelectedIndex", report , "MyClass", true, DataSourceUpdateMode.OnPropertyChanged, -1);
            cbClass.DisplayMember = "ClassName";
            cbClass.ValueMember = "Id";
            cbClass.DataSource = bsClasses;

            cbStudent.DataBindings.Add("SelectedIndex", report , "MyStudent", true, DataSourceUpdateMode.OnPropertyChanged, -1);
            cbStudent.DisplayMember = "Students.Name";
            cbStudent.ValueMember = "Students.Id";
            cbStudent.DataSource = bsClasses;

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