I really need help for my friend. I know next to nothing about computers.

My roommate and I both have macbook pros from the same year running OS X, are both connecting wirelessly to the same xfinity wifi, and while mine runs perfectly fine, my roommate complains that his works very slowly and times out every few seconds. I can't seem to figure out why this is. He is trying to get me to switch internet providers because he is convinced that it is their problem, but this cannot possibly be the issue since it works great on mine. He has an xbox hooked up to the wifi that he says also works poorly.

I really can't see switching providers given that I am experiencing absolutely zero problems. How can I help my friend?