Pass A Parameter To A SqlDataSource

I'm trying to pass my SqlDataSource a parameter that is defined in the code-behind file for the same page.  I've tried the method below but it does not work.  Is there a better way?

SubmitForm.ascx page: 
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ connection string...... %>"
    SelectCommand="sp_CourseMaterialShipment_GetCourses" SelectCommandType="StoredProcedure">
    <SelectParameters>
        <asp:Parameter DefaultValue="<% ProgramID %>" Name="programID" Type="Int32" />
    </SelectParameters>
</asp:SqlDataSource>
 
SubmitForm.ascx.vb page:
Private ProgramID as string = "25"

Public ReadOnly Property ProgramID() As String
        Get           
            Return _ProgramID
        End Get
End Property

 
Thanks
Jason