Math Addition Facts

Gabriel is learning his math addition facts for timed tests, which means he should know the facts by rote. He should be able to answer 25 in 2 minutes. But I find that he is counting on his fingers which is slowing him down. He has managed to pass the 0's and 1's and is now working on the 2's. But I feel like I am pulling teeth trying to get him to work on this. He is stressed about it. When he can't pull it out fast enough he hits himself on the head like that would help pull the answer out faster. I don't know if this is because I have put too much pressure on him or if he is putting it on himself. I have tried all the techniques that I learned while in school and tried a few I have found online. But I need help in finding fun and exciting ways to teach him his sums without the stress. So, if anyone has any awesome suggestions on how to make this task more fun I would love it. Or if you know of any great games for teaching this that would be great too. And Thanks.