Teach them the basics about fabric and how to cut accurately and importance of quarter-inch seams. Then if you teach them how to make HST's, quarter-square triangles, flying geese, you've pretty much taught them most everything they need to make a beautiful quilt that is easy but looks terrifically (sp?) hard!!!
Also, tell them they don't need 20 different rulers. Maybe if you could have a selection of different ones they might try. And I used to work in a quilt store and people would come in to buy a 6" square up ruler and then a 9" and then a 12". My advice to them was to buy the 15" or 16" and then they could square up all sizes. Of course you need a smaller square to cut other things but do tell them not to get sucked in to all of the "specialty" rulers. Some of them really don't make things easier.