I don't have experience with the ajax tags so I don't know what the easiest way to display that URL is, but I think its pushed onto the stack, so I think you can use an <s:property value="student"/> to write it out.
Using the interface isn't enough to make model driven work. You need to use the modelDriven Interceptor as well (its what calls getModel on your action class to put the model on the stack). If you don't have this interceptor in your stack I don't think your model will get populated. To
test you can put a println in your getModel method to see if it ever gets called (unless you wrote some code to call it).