First, I have to admit I figured this out with a "light-bulb" moment while working on some basketball kits I'm designing. I just had to stop to share what I discovered.
Start with sketches on some kind of drawing paper (a paper that will have a bit more texture to it than regular white computer paper) or from a sketch book like I did. And, yes, I used one of my kids pencils.
Scan your sketches and save on your computer.
Open in Photoshop (for this tutorial I'm using Photoshop CS6).
Now your background looks like a black chalkboard and your pencil drawing looks like white chalk.
Bonus: even where I smudged the pencil - it looks like white chalk dust
I hope you are as excited about this discovery as I am!
Thanks to Lana for this help with anyone using PSE11:
Click Enhance>Adjust Color>Remove Color
Click Layer>New Adjustment Layer>Invert
Click Layer>New Adjustment Layer>Brightness/Contrast