I just looked at the pattern you want to use, and while the instructions are certainly copyright protected, the design of the tree skirt would not qualify as sufficiently original work to itself be copyright protected (IMHO). What that means is that you can write your own directions (being very careful not to copy any of the directions from the original pattern - in fact don't even refer to it while writing) and use those directions for your class. When I took my first quilting class, the instructor had done that, although I have to admit her writing was not that clear, and I would have preferred to have purchased the original pattern.