|Got it, first try...|
I did a little pre and post test for my 8th grade during value drawing this quarter. I really gathered some good data and changed my instruction because of it. Students were asked to add value the top objects on this worksheet. They turned it in as a ticket out the door. I took a look at them that night and determined what drawings were successful with out in depth instruction and what students could use a bit more direction.
My first class almost all students had the concept already so I gave had them get started on their project and took a very small group aside and had a little private lesson. They then created value on the second set of objects. My 3rd class of the day had most of the class without the skills at that time, so I did the opposite. I got my small group going on the value drawing and instructed to the large group.
You can see that there is improvement from fist drawing to second drawing in both of the examples above. The first one had the shadow disconnected from their object. You can see that the second object include the shadow next to the object. The shadow was on the wrong side but that was my fault... in order to instruct I took a image of the object and the shadow and took it from the wrong direction. Oops:) The second example above had very light value and that is why I asked for a retry. That student was much more successful the second time!
I found the pre and post test to be very valuable to lead my instruction.