Working on problems like 11+7= and 9+9=, we made it pretty simple. Mad Natter has a large love for all things Legend of Zelda. So, I asked him: If you had eleven hit points, and picked up a heart for seven more, how many hit points would you have? Well, all of a sudden, this was fun and entertaining! He would ask to do more math! It was a huge breakthrough! Then, we started subtraction.
Would hit point math work for subtraction? Only one way to find out. Sure enough, one round of "you have 25 hit points. You take 11 points of damage. How many hit points do you have left?" and he's all about the subtraction, too! Oh, happy day, no more fighting over math!
Then... we moved into three double digit number addition. He could do it, no problem, but it wasn't anything he wanted to do, so... More hit point math? Something like that. We jumped to video times instead, figuring to vary things a little. So then we had "you watched a 25 minute Stampy video, a 12 minute EthanGamerTV video, and a 35 minute mod review with Pat and Jen. How long have you been watching videos?" It's like the storm has cleared, and the sun is shining on our school table. How I managed to handle math before we tried this, I'll never quite understand. But I'm so very glad we found it, 'cause it's made our lives so very much easier!