Paris and environs.

The Museum of Science and Technology, www.cite-sciences.fr, a visit to the FNAC music store one the Champs-Elysees, Ice Cream at Berthillion, a Segway tour, Tour of the Sewers, (http://www.parismuseumpass.com/musee-musee-des-egouts-de-paris-23.htm) and a visit to the Deyrolle Taxidermy shop on rue du Bac.

Speaking as a 13-year-old boy (NOT! :-) - but based on my memories of being a 13-year-old tomboy - I'd recommend the sewers, the catacombs museum, the army museum (I believe this includes the Napoleon museum and the Musée des Plans-Relief), a picnic/afternoon hanging out at Beaubourg (where there are local teens to socialize with), the Carnevalet (Napoleon's death mask, a mammoth tooth, cool old Roman stuff) and climbing up the stairs at Notre Dame to check out the gargoyles.

Paris also has a decent lookikng aquarium.

Well having taken my own oldests son when he was 13 these are the things he liked. The Catacombs,, big highlight for him. Eiffel Tower, the stairs too,, he ran up like a bunny. The Towers of Notre Dame,,whew, moms tired.Ver The Invalids Army Museum The Louvre( yes, he loved it, I love it so I knew the parts to visit with him, and it did not revolve around the "big 3"!)
Versailles( he had just covered the revolutions in school that year so felt he could relate to a bit of what he was seeing) I also suggest you look at taking him on a Fat Tire Bike tour, they are fun and easy.. A great daytrip to Versailles, Giverny, or just the paris tours, they are fun and lively,, and as I said, easy. I also made each one of my kids( have 3 who all got seperate trips) look up Paris and tell me which 3 sites interested them, thats how I found out about the Catacombs,oldest boy found them on the web!

I suggest the Champs-Elysees walk as in RS Paris book but I like
To do it backwards to walk toward the Arc de Triomphe. There are several car dealerships, Peugot has classic cars & futuristic ones too, Mercedes & Renault also. There were lots of tourists in Peugot. If he is into funky sneakers, there was a huge ? Nike or Puma store also along the Champs. Perhaps a picnic in the Champs du Mars park beside the Eiffel Tower. Although you cannot enter the Ecole Militaire, seen at the end of the park, if you go to the gated entrance (not facing the Eiffel Tower) they are often exercising gorgeous horses that can be viewed through the gates. Perhaps visiting one of the more lively open air food markets, Bastille or Richard Lenoire, where you are likely to see the pig head, trotters, whole chickens with head and feet still on , all on display for purchase. I had a picnic at a lovely park, I think along Richard Lenoir where school kids were playing ping pong at outdoor tables and kicking around a soccer ball. Parisiens use their park spaces almost daily. Perhaps he would like the Orsay Museum as it was a train station. I recently saw a movie about a young orphan boy whose job it was to wind the clock there, not sure of the name. The big clock astounds me. Have a great trip.