Wow. Are you free to teach at my house? The Chickadees all need remedial math this summer :-(.
The quality most needed is a passion for ensuring the kid learns, which in most people is easier to develop for your own kid than for someone else's
In my case, it helped a lot that I had an engineering education, but the main thing needed was the attitude "I don't care if you think you can't do it, you WILL learn this @#%$ if it kills the both of us !!!"
In addition to that, the main thing you need is the understanding that math is a progression that depends on the full understanding of the earlier fundamentals. Meaning if you cover topics A, B, C and hit the wall at D, then you need to go back and review A, B, and C to find out what was not fully understood, instead of both of you getting frustrated at D. In other words, the trouble comes from the earlier material that the kid thought he understood.