Exploratorium
Parabolas
A parabolic mirror toy demonstrates how concave mirrors objects reflect light and produce a realistic image at their focal point. This resource probably doesn't explain any more than the printed insert that accompanies such an apparatus...
Exploratorium
Hot Spot
Not only does a concave mirror focus light waves, it can also concentrate infrared radiation into a hot spot. If you have a small electric heater and such a mirror, demonstrate this for your physical science class.