Private Sub Form_Open(Cancel As Integer)
For Each ctl In Me.Controls
    If TypeOf ctl Is CheckBox Then ctl.OnClick = "=ChkBx_Click([" & ctl.Name & "])"
Next
 
End Sub
 
Public Function ChkBx_Click(ByRef ctl As Control)
SeciliSay = 0
With Forms!ogrenciler!sinifi
    .Enabled = True
    For Each ctl In Me.Controls
        If TypeOf ctl Is CheckBox Then
        If SeciliSay > 0 Then .Enabled = False: Exit Function
            If ctl.Value = -1 Then SeciliSay = SeciliSay + 1: .Value = Val(ctl.Name) Else .Value = Null
        End If
    Next ctl
 
    .Enabled = False
End With
End Function