The greatest failure of our time is that there isn't a viral, ad-free website or app for children and teens to just go and learn math on their own. Everything worthwhile requires a credit card, user account, and monthly subscription. Children don't have credit cards, email addresses, and access to the latest iOS device. They do have time and at minimum sporadic Internet access. If we managed to create Wikipedia, we can manage to create a similar site for enjoying and learning math.
Khan Academy is close enough to what you describe, and it covers K-12 plus some college-level courses. If anything, it's a lot easier to achieve this wrt. math than many other school subjects.
This. Between Khan Academy and youtube, there isn't really anything stopping a motivated person from learning. Hell you can get graduate level instruction from some of the best university instructors around by using some of the open courseware materials. Granted some people need the rigor of having an instructor assign and grade assignments regularly, but there are no real barriers to the information itself.
plenty of learning resources exist. kids just don't have the motivation or focus. i'm not saying the kids are at fault though. there are a thousand games/apps that are like nicotine.
Khan Academy is limited to learning by boring examples (IMHO) in lecture format and does not virally engage a learner with play. It's analogous to a free virtual classroom.
