using ajax4jsf with dropdawn list

I have two drop dawn lists, I need to change the second one options depending on the selected value in the first one using ajax4jsf

I wrote the following jsf page

<f:view locale="en">
        <head>
            <title>Account Details</title>
        </head>

<body>

<h:form id="form">
                 <h:selectOneMenu styleClass="tbflat" id="studentlist" value="102">  
                <f:selectItems value="#{accountSearcher.students}"  />
                <a4j:support event = "onchange" immediate="true" 
                    actionListener = "#{accountSearcher.changeDropdownItems}" 
                    reRender = "studentlist1"/>
                </h:selectOneMenu>   
                <h:selectOneMenu styleClass="tbflat" id="studentlist1" value="102" binding="accountSearcher.newValues">  
                <f:selectItems value="#{accountSearcher.students}" /></h:selectOneMenu>   
        </h:panelGrid>

</h:form>
    </body>

</f:view>

</html>

and the bean

but it doesn't work so any body can help me with my problem?