Calculations about spectra and spectral lines should be left to college. But even primary school students can look at the light through prisms and gratings and see how light separates into its component colors. Middle-grade students can look at vapor lamps through gratings and notice how the pattern of bright, emission lines is the same when the element is the same. They can also discuss the difference in appearance between the spectra of incandescent bulbs and neon bulbs. A number of words are associated with the term spectrum .
Many Internet sites provide information about spectra.
Unfortunately, most are esoteric, intended for practicing astronomers. These two, however, may be of particular interest. Look here for a history of astronomical spectroscopy. And check here for physics lecture notes that explain absorption and emission lines in stars. Of course, you will see the light itself.