First, are there any activities your dog likes that could become a game for your 7-year-old? I only ask because we had a Great Dane who had been malnourished before we got her, and we think had some brain damage as a result. She was sweet as can be, but never "got" fetch. Or even "catch" - not even for food! We loved Gracie, even though we had to give up on certain things with her.

But does the dog respond to squeaky toys? Or food? What makes him interested?

If you can find something that piques his interest, you can try to teach fetch. Get him interested - I'll use a "squeaky toy" as an example. Have the dog on a leash, next to you. Tell him "sit" and then squeak the toy a few times so he is interested. Toss the toy a few feet away and let him go get it, then using the leash, encourage him to bring it back to you. It may take a lot of repetition, but even your son can help train him.

With Gracie, the one "game" she liked was "kill the leash" which in retrospect wasn't the smartest thing to play, but she enjoyed it, so we went with it! When she was on the leash, we'd shake it a little, and she'd "attack" and "kill" it, shaking back and forth, growling and in general looking quite silly! I only say it wasn't the smartest game because we did go through more leashes than with any other dog, and in public, have a huge black snarling growling beastie was not always a good thing - people would ask if I was in danger or needed "help" - but hey, she had a good time!