I know you didn't ask for advice on whether or not to get a dog, but I just wanted to throw in my two sense.
I got my son the sweetest rescue dog the summer he was 10. I wanted an adult dog, and he was about 15 months when we got. He's pretty small (25 lbs) cuddly, happy little guy. I really do like him,
But it's also one of my biggest regrets. When my son was 10 and 11, it was perfect. My son spent hours playing with him afterschool, he came with us to soccer practice, and soccer games, and we'd spend our weekends hiking or going to a dog park or other things. Lots of fun.
The middle school years were pretty good too. The older kids play on turf, so he couldn't come
But now, I have a high schooler. With sports practices he's gone at school for 11 hours a day, and that's if it's a day when he doesn't have a Dr.'s appointment after that (1 day a week) or a match (1 or 2 days a week) or just want to hang out with his friends. He's really good about caring for the dog when he's here, but there are lots of days like yesterday, when he walked the dog, and left for school at 7 a.m., and then didn't get home from a tournament until midnight. My first choice for the evening would have been to head to the mall to get Christmas gifts, or maybe even see a movie of my own, but instead my schedule was dictated by the dog.
In 4 years my son will be out of the house, and the dog will be 9. If we're lucky (and I say that because I do love him) I'll have another 5 or so years to be tied down.
So, my advice is to think about a rescue mutt (mine is a "big dog" personality in a little package, he's really the perfect dog), but maybe think about getting an older dog.