Could hydrogen peroxide whiten teeth?

Yes, but...: Yes, but in higher concentrations than is usually available over the counter. For example, most hydrogen peroxide available in the store is around 3%(or 4), the strength needed to effect bleaching on the top layer of the enamel(about 75 angstrom, very thin) is more on the order of 20 to 30%. This concentration can be very caustic to the soft tissue, and is not readily available to the consumer.

Bad idea: Yes, but don't do it! it is not very effect in its over the counter form. And can cause more harm than good. There is a rarely used, very potent solution used by some dentist to bleach root canal teeth.