I don't think Sacramento will thrill teenagers that much. San Francisco has China Town, lots of history, very pretty.
Portland is right on the river, will they be able to go skiing on MT Hood? It's smaller but very nice. Valdosta has the Wild Adventures Theme Park, antibellum homes, old Southern charm, I'm not sure what the teenagers would be interested in. How much time will they have? It isn't that far from Orlando, Florida where the theme parks are so much better than in California. Surely your school has gathered all this info for the kids and parents. Are they flying everywhere or traveling overland so they can see the US? I hope they really enjoy their trip.