I want to insert class_ID column Dropdownlist selected value into database, but value is inserted 0.

public class SaveDataController : Controller
{
    // GET: SaveData
    public ActionResult Index()
    {
        tbl_Student student =new tbl_Student();
        student.ClassList = GetClasss();
        ViewBag.saveresult ="";
        return View(student);
    }
 
    [HttpPost]
    public ActionResult Index(tbl_Student student)
    {
        using (SchoolEntities2 entities =new SchoolEntities2())
        {            
            student.std_id = student.std_id;
            student.std_Name = student.std_Name;
            student.class_ID = student.class_ID;
            entities.tbl_Student.Add(student);
            entities.SaveChanges();
            ViewBag.SaveResult ="Data Save";
            ModelState.Clear();        
        }
    }
 
    private static List<SelectListItem> GetClasss()
    {
        SchoolEntities2 entities =new SchoolEntities2();
        List<SelectListItem> classList = (from pin entities.tbl_Class
                                          selectnew SelectListItem
                                          {
                                               Text = p.Class_Name,
                                               //Value = p.Class_ID
                                               Value = SqlFunctions.StringConvert((double)p.Class_ID)
                                          }).ToList();
 
            //Add Default Item at First Position.
            classList.Insert(0,new SelectListItem { Text ="--Select Class--", Value ="" });
            return classList;
        }
    }
}

<div>
    @using (Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        <table border="1" bgcolor="yellow" width="400px" height="250px">
            <tr>
                <td>Roll Number</td>
                <td>  @Html.TextBoxFor(m => m.std_id, "{0:#.#}")</td>
            </tr>
            <tr>
                <td>Student Name</td>
                <td>  @Html.TextBoxFor(m => m.std_Name)</td>
            </tr>
            <tr>
                <td>Class</td>                   
            </tr>
            <tr>
                <td colspan="2">
                    <input type="submit" value="Submit" />
                </td>
            </tr>
            <tr></tr>
        </table>
    }
</div>