How to Make Grandpa's Hair
Buy 1/4 yard of fake fur at your local fabric store. Choose white, brown, or black (whichever you think looks like hair.) It's expensive, but 1/4 yard is all you need and this amount will yield several "wigs." When you cut this product, remember to part the fur so it doesn't make a mess when you cut through it. Once it sheds around the edges, it will stabilize.
Cut a square of fur this approximately 10 X10 inches. Trim the corners to create a circle. You can also trace a circle on the back using a plate as a template.
You can use it like this, or you can make it more "wig-shaped" by taking 3-4 tucks in. In the illustration below, I drew four triangles, folded them in half, and sewed them to create the tucks. You can also staple them if you wish, but if you plan to let students take it home, it's best not to staple it for safety reasons.
For hygienic reasons so the students don't attempt to wear it, you can make it smaller so it won't fit their heads, and/or line the inside with duct tape which can be wiped off.