This a 3rd Grade lesson for pounds and ounces.  It is student centered.  The students make up their own problems and use the keyboard shortcuts for copy and paste to create enough “weight” pieces to complete their problem.  You kids can animate the slides as well.  There is an exported example with animations and the template below.

[local /wp-content/uploads/2009/12/lbs-ozsblog.mov]

Click here to download the template.