Dropdown Selected value of user control on Page Load

Hi
 I have a function on page load which will work based on dropdown selected value. and I am using this dropdown in a user control.  So  getting problem because the dropdown value is not loaded yet before Page Load.  How Can I do that using those control still...Have any idea?
Here is my code below............
public partial class GradeEntry : System.Web.UI.Page
    {

        StudentManager studentManager = null;
        CourseManager courseManagerObj = null;
        GradeManager gradeManager = null;

        protected void Page_Load(object sender, EventArgs e)
        {
            
            if ( ...