JQuery Validate Plugin MS MVC Won't Validate?

I'm trying out the jQuery Validation plugin jQuery Docs Here is the markup of my form:

<% using (Html.BeginForm("action", "contoller", null, FormMethod.Post, new { id = "sxform" })){%>
<div id="manifest">
Manifest Option:<br />
<%= Html.DropDownList("docid", ViewData["manifests"] as SelectList, new { @class = "required" })%>
</div>
<div id="release">
Release Version:<br />
<%= Html.TextBox("release", null, new { @class = "required" })%>
</div>
<div id="locale">
Localization:<br />
<%= Html.DropDownList("localization", ViewData["localizations"] as SelectList, new { @class = "required" })%>
</div>
<div id="label">
Label:<br />
<%= Html.TextBox("label", null, new { @class = "required" })%>
</div>
<div id="session">
Session ID (optional):<br />
<%= Html.TextBox("sessionInput", null, new { @class = "required" })%>
</div>
<div id="submit"><input type="submit" value="Build" /></div>
<% } %>
JS:
$(document).ready(function(){
$("#sxform").validate();
});

I am using MS MVC HTML Helpers to render this form. The resulting markup looks fine. IE each input and selection element contains the attribute 'class' with the value 'required'. When I submit this form the validation does noting.