Pokémon FireRed and LeafGreen/Route 14-15

After passing through Routes 12 and 13, you'll end up in Routes 14 and 15.

Share and Share Alike
Just before returning to Fuchsia City, go to the lookout station above where the guard stands and talk with the Professor's Aide. If you have caught more than 50 kinds of Pokémon, he'll give you the EXP Share! Unlike the EXP All in Generation I, this is a hold item, and only the held Pokémon shares the experience with the Pokémon that battled. This is much less time-consuming and aggravating than having to go through six EXP screens, though.