Some people really just don't get this. And, VAK confusingly can be applied to preferred learning style, as well as to natural communication style. This tool is for preferred LEARNING style. (for VAK communication style assessment see my other post: Free Online VAK Communication Style Preference Assessment)
Give this link to the coachee: http://www.vak.solida.net/. Again I think the best time to do the assessment is in the morning, before work really starts.
When the assessment is complete, you will have the 3 styles - Visual, Auditory and Kinaesthetic in the coachee's preferred sequence.
You now have material you can use to support the coaching goals and plans where learning is required. You also have the approach you need when explaining concepts to the coachee - a real time saver and much more enjoyable experience for you and the coachee as compared to approaching from the worst angle. And even more enjoyable if you're going to have to explain in your non-usual communication style. Personally, once I realised what my preferred/natural learning approach was, I realised why I was bored out of my skull and kept falling asleep in school and university lectures. Really useful stuff!