As to the long division, I would encourage him to continue to practice the mental skills. Then use the long division only as explanation or proof. I'm still a little peeved almost forty years later that school broke my ability to do complex division quickly in my head when they forced me to do long division. I think at some point later I would've understood it well enough to bullet proof it against their methods, but without continuing to use it I lost it. It didn't occur to me at the time that I would need to do something to preserve the skill.
