I'm a huge fan of online learning, and Coursera seems to be doing the best in this at the moment. I'm already signed up to courses in biology, maths, and linguistics, but I thought I'd bring your attention to some of their latest music offerings, taught by people from the Berklee College of Music, the University of Florida, and Emory University:
How Music Works
Introduction to Music Production
Introduction to Improvisation
Introduction to Digital Sound Design
Introduction to Guitar
Each course has a start and end date, some with assignments during, though you have flexibility to watch the lectures whenever you like once they're uploaded. Some will also give you certification upon completion of an end-of-course exam.
If you're interested in other subjects, check out coursera's 100+ courses for fantastic lecture series on all the sciences, maths, humanities, business, economics - you name it! Most courses don't require any previous knowledge, though I've seen at least one or two in medicine that are designed for graduates.
I realise I sound like an advertisement, but I'm just passionate about free education.