I've created a Brush in Dry Media called Scrumming Chalk, that will appear under the Chalk brushes.
To install it to the following
1. Save the following file to Program Files\Painter7\Brushes\Painter Brushes\Dry Media (assuming you chose the defaults on installation). Be sure to preserve the .XML extension or the brush will not work.
2. The brush will now show up under the charcoal brushes.
To use the brush, you must first choose the paper that contains the template for the brush.
You may want to play around with the scale and contrast settings to get more or less definition.
Then Select the color from the color palette which will serve as the color for the effect.
Next Create a Layer in the Objects Menu, and begin Drawing. I like to use layers in this case since if I blow it I can simply delete the layer. I can also create textures to just the scrumbling and also choose how to merge the layers.
You will want to set the paper grain pretty low to get more of the "skipping" effect shown here. Also play with the opacity in the Brush controls to get more or less color.
This shows using the Default Composite Method
This is the same layer using the Overlay Composite Method.