Scratchboard is a form of art, where you have a nice smooth unblemished surface and you scratch your drawing into it.
Usually this is a stiff board, with a layer of white wax on it, covered with a layer of black India ink. Many companies make prepared scratchboard for you in various sizes.
You can make your own.
When you are working larger than card sized, you do want to use a stiff support. The layer of wax means that if it flexes a lot, it can crack and peel. Something you don’t want if you work very hard and achieve really good results.
For my drawing classes, we made our own scratchboards. We used card stock. Stiff enough for the first try.
Covering them with hot wax and getting a smooth layer could be a problem with a junior class. Also, a bit boring.
Instead we are using oil pastels.
Cutting the cardstock into 2 pieces. We do have a support that is large enough to work on, but not so large that the piece will over flex and crack a lot.
And covering it in oil pastels was a lot more interesting.
Using a standard precut mat, we drew a rectangle that will contain our masterpieces. This also gives us a large margin for handling the material without compromising the scratchboard surface.
Also, using a bright, light color will make the finished pieces more interesting for the class.
Choosing a light color, we colored in our rectangle. After it was filled in, the surface was checked for missed areas (much easier to do with a color than white wax) any missed areas are fixed, and the whole thing smooth with a chamois cloth.
Then a layer of good India ink was used. Something permanent is necessary for this.
It does require 2 good coats, one in each direction to get a good coverage. If you have used more than one color for your scratchboard, you can mark the card with the top.
India Ink should set for at least 24 hours before you beginning scratching a drawing into it. It does work better with some time to cure.