My Granddaughter is 15 and has a yellow spot right in the center of her front tooth. It will not come off!! What can we do to whitten thi spot?

Find a dentist and have her teeth cleaned and the teach her how to keep her teeth clean.

The chances are that if this yellow spot is only on that one tooth and the rest of her teeh are OK, that it may not be a stain at all and the beginnings of tooth decay. Either way as Tickle suggested it's time to see a dentist.