This is a very quick and easy way to show kids that white light is made from a rainbow of colors. A students needs no assistance in using it -- you just tell them to look at a light through it. I like it better than a glass prism because you don't have to worry about a child dropping this.
Make a Shoebox Spectroscope
After using a shoebox spectroscope at a planetarium, I decided I had to have one for myself! Uh, I mean for the kids, for the sake of their education. I found instructions on the Internet and went straight to Home Science Tools to order the diffraction grating. I ordered a pair of shoes elsewhere (I needed them, really). It was very easy to make and we used it to look at the spectra from light bulbs, street lamps, and burning salts (along with Home Science Tools' Spectroscope Analysis Kit).