<div id="dd1" class="dd-demo"></div>
<div id="dd2" class="dd-demo"></div>
<div id="dd3" class="dd-demo"></div>

$('#dd2').draggable({
 proxy:'clone'
});

$('#dd3').draggable({
 proxy:function(source){
 var p = $('<div class="proxy">proxy</div>');
 p.appendTo('body');
 return p;
 }
});

<div class="left">
 <table>
 <tr>
  <td><div class="item">English</div></td>
 </tr>
 <tr>
  <td><div class="item">Science</div></td>
 </tr>
 <!-- other subjects -->
 </table>
</div>

<div class="right">
 <table>
 <tr>
  <td class="blank"></td>
  <td class="title">Monday</td>
  <td class="title">Tuesday</td>
  <td class="title">Wednesday</td>
  <td class="title">Thursday</td>
  <td class="title">Friday</td>
 </tr>
 <tr>
  <td class="time">08:00</td>
  <td class="drop"></td>
  <td class="drop"></td>
  <td class="drop"></td>
  <td class="drop"></td>
  <td class="drop"></td>
 </tr>
 <!-- other cells -->
 </table>
</div>

$('.left .item').draggable({
 revert:true,
 proxy:'clone'
});

$('.right td.drop').droppable({
 onDragEnter:function(){
 $(this).addClass('over');
 },
 onDragLeave:function(){
 $(this).removeClass('over');
 },
 onDrop:function(e,source){
 $(this).removeClass('over');
 if ($(source).hasClass('assigned')){
  $(this).append(source);
 } else {
  var c = $(source).clone().addClass('assigned');
  $(this).empty().append(c);
  c.draggable({
  revert:true
  });
 }
 }
});