Amanda,
Here is an initial idea of best parks by day, taking your Advanced Dining Reservations into consideration;
- July 26 - Magic Kingdom
- July 27 - Animal Kingdom
- July 28 - Hollywood Studios
- July 29 - Epcot
- July 30 - Hollywood Studios
- July 31 - Magic Kingdom
- August 1 - Epcot
- August 2 - Magic Kingdom
If you don't plan on hitting a park on the 2nd (because of an early departure time), you could move Magic Kingdom to the 1st, and visit Epcot on the 31st. This should help you plan your days, getting in three days at the Magic Kingdom, and two each at the Studios and Epcot, which should both be great choices for you, especially with a pre-teen.
I would also recommend that you consider visiting Downtown Disney some day. Rather than scheduling it in, visit there on whatever day has you getting a bit tired of being in a theme park. It will be a nice change of pace!
I am glad to help you plan further, like meal recommendations by park, if you would like. Just send me another question with the parks you plan on hitting each day.
Have a magical vacation!