Hello I do not know if anyone has worked with soft pastels but we love them. What we love is how easy they are to draw with and how wonderful they are for layering colors. I took a class a long time ago about how to get children interested in art. She recommended soft pastels. You start either with light and go darker, visa-versa. You make a basic shape like an oval and start adding to it. Lets say a fish, add smudgy fins, face, ect. Then finally add strokes to define your picture. It is amazing how much detail there is for little effort. This is why this is good for a reluctant artist.
I love them because I love to smug all my colors together and these blend so beautifully. The soft pastels we use is a 60 box of half sticks by Rembrandt. I know they are a bit pricey but they last forever. I found them for a very good price at Blick. If you want to set the pictures so they do not smudge, spray them with hairspray. But this does darken the colors a bit.
Now to my post I found this wonderful old book Blackboard Sketching by Fredrick Whitney. He is sketching with chalk on a chalkboard but uses the same technique I was talking about. I think the soft pastels would work wonderful with this book. I found Blackboard Sketching very charming and inspiring. My favorite combo !!!