I am editing a forthcoming book in the field, written by a teacher who earnestly believes in MI. Evaluating this teacher's data, his approach is clearly working for his students, but I think because of better engagement, more individual attention, and more interdisciplinary projects. Ultimately, I think we're cutting most of the MI stuff from the book as unsupported, although he will cite Gardner as inspiration.

The data I've looked at is more consistent with variation in subject performance primarily correlating with interest and personality, rather than MI.