Insert Rows Into Subform Problem, Help!

hi i have a main form called "frmMain" that i use for users to add new studentsNumbers txtStudentsNumbers.bound to tblStudents also this form has a combo box called cmbDepartments coming from tblDepartments.

Then a subform which right now it has a combobox called cmbSubDepartments (coming from tblSubDepartments) , this combobox has a rowsource to update everytime someone selects a dept in the main form so it shows the subdepartments belonging to the departments.
Each department has a a set of Subdepartments, also has two texboxes called txtTuitionA, and txtTuitionB.
so in total i have three tables each with the pk id.



what i need is that when a user enters a student number in the main form, select the department where they want to add the student to, then the subform gets automotically populated with all the subdepartments so then the user is forced to enter TuitionA and tuition B to each subdept for that particular students

i tried this...

(in the main form)

Private Sub cmbDepartment_AfterUpdate()
Dim intQty As Integer
Dim i As Integer


If MsgBox("Are you sure you want to add a new tuition plans for this student?", vbYesNo) = vbYes Then
Me.txtStudentID = DMax("StudentID", "tblStudents") + 1 'get New student number 'Add the new row into Main Table tblStudents

intQty= me.cmbSubDepartments.itemdata -1

For i = 1 To intQty - 1
strSQL = "INSERT INTO tblStudent (StudentID, SubDepartmentID) SELECT StudentID, SubDepartmentID FROM tblSubDepartments WHERE SubDepartmentID = " & Forms!frmStudentsTuitions_subform!cmbSubDepartment s & ";"
CurrentDb.Execute strSQL


Next i

Me.frmStudentsTuitions_subform.Requery
Me.frmStudentsTuitions_subform.SetFocus



Else
DoCmd.CancelEvent 'if user choose no in question then undo
DoCmd.Close acForm, Me.Name 'close current form

End If


End Sub


but my subform does not get updated... :-( .