I have also sprayed things gray and used a single light source over it. This was easy for them to see the different values of grays...and also the highlights.
We set up a still life using things that were white-paper cups, pottery, molds, silk flowers, toilet paper rolls, mat board, paper bags, vases. We used a "cubby" in the art studio, hung different white fabrics or board, covered boxes to vary heights, and then just filled it up-including tacking some things onto the walls. We attached a single light source over the top (that we could adjust the angle). Students used a view finder to help decide on a section to draw. They came out great! Next year we will build a black still life.