Brian Marick certifies that Ron Jeffries is, at a minimum, qualified to teach others the skill coaching, based on this evidence:

I've had two multi-trip coaching engagements where I worked with Ron. I learned a lot about the craft of coaching by watching him coaching teams.

Consider once when I was pairing with one person while Ron was pairing with another:

I was having a frustrating time because my pair and I were butting heads about design decisions. Out of the corner of my ear, I heard Ron say "Well, let's try it your way" to his pair. That caught my attention because Ron isn't famous on the net for backing down from his opinion. When I asked him about it later, Ron said that he was sure his proposed design was better but that (1) he was pretty confident that they could start off down the wrong track, get messed up, and then bend the design the right way without any major fuss; and (2) that it would be even better if he were wrong about the design -- because then he'd learn something.

I've consciously taken that attitude in my own consulting, to good effect. I also learned something about Agile, which is that it's in part about arranging your universe so that the consequences of being wrong aren't a big deal. That allows you to keep being less wrong - which makes you faster than people who care too much about getting it right, right now.