public class StudentModel
    {
        public IEnumerable<SelectListItem> NormalStudentsList { get; set; }
        public IEnumerable<SelectListItem> StudentsNoClassList { get; set; }
        public string[] NormalSelected { get; set; }
        public string[] NoClassSelected { get; set; }
        public string Save { get; set; }
    }

public ActionResult IndexStudents(Docent docent, int id, int klasgroepid)
        {
            var studentModel = new StudentModel
            {
               NormalStudentsList = docent.GeefStudentenNormaalList(id, klasgroepid),
               StudentsNoClassList = docent.GeefStudentenNoClassList(id, klasgroepid)
            };

            return View(studentModel);
        }

        [HttpPost, Authorize]
        public ActionResult IndexStudentsResult(StudentModel model, string add, string remove)
        {
            ModelState.Clear();
           (if! string.IsNullOrEmpty(add))
               //update database
            SaveState(model);
            return View(model);
        }

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master"  Inherits="System.Web.Mvc.ViewPage<ProjectenII.Models.Domain.StudentModel>"%>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
    IndexStudents
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <h2>IndexStudents</h2>

  <%using (Html.BeginForm()) { %>
    <%=Html.ListBoxFor(model => model.NormalSelected, new MultiSelectList(Model.NormalStudentsList, "StudentNummer", "Naam", Model.NormalSelected), new { size = "6" }); %>

    <input type="submit" name="add"
                          id="add" value=">>" /><br />
    <%=Html.ListBoxFor(model => model.NoClassSelected, new MultiSelectList(Model.StudentsNoClassList, "StudentNummer", "Naam", Model.NoClassSelected)); %>
  <% } %>

  <%=Html.HiddenFor(model => model.Save) %>
  <input type="submit" name="apply" id="apply" value="Save!" />
</asp:Content>