To Mark's point...
I just went through this and why I suggest backchaining from extension back is that you can easily alter pitch location by moving the tee (don't even use a ball)...
There is tons of stuff in the DBSF thread that is loaded with clips from JJ's DDs, Perfect Circle's DD and my DD2...
Start here for extension: http://www.discussfastpitch.com/softball-hitting-practical/25763-dbsfa-drop-barrel-swing-flat-anonymous-fff-thread-48.html#post359808
Getting them to feel what "whip to extension" feels like was easiest for us going from extension back to contact - then whip...extension back to launch - then whip...extension back to load - n whithep, etc all the way back to the handset and then repreating this for multiple pitch locations has been key to my DD's 8 week "transformation."
I'm not saying it's the be all-end all but we had great success with this in terms of getting her to and through extension...CP
Chris, Pls bare with me. I just want to make sure I get this right. When you back chain, do you pause at each point and go all the way back to the start of the swing? Or do you stop at a certain spot then go forward? The points to emphasize are extension,poc,whip, load (hip coil) and start. Can you pls clarify for me?
Thanks