I'm working on a music theory class for my bandmates in the Austin Civic Wind Ensemble. Most of them have not studied music after high school (although quite a few have). But they all know how to read music and play an instrument.
That's why most of the music theory books and online classes just wouldn't work. They either start at a very remedial level (what is a staff? What are whole notes?), or at a level too advanced for us. I want to tailor the class to band geeks who play.