passing element id to php through JQUERY

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PHP

jQuery

I'm trying pass a html element id (from a td actually) through JQuery to a php page. The JQuery function i'm using is:

$(document).ready(function(){
               $("td").click(function () {
               alert($(this).attr('id'));
               $.post("index.php?p=lesson", { id: $(this).attr('id') }, function (response) {
                   alert(response);
               });
           });
         })

and the call in the php page:

$lessonPath=$_POST['id'];

but the variable i'm passing the the value in php page doesnt get a value at all.
Any ideas?