I would never have had the time to create the infrastructure for assessment and teach my overload schedule... probably not even with decent release time... khanacademy.org has LOTS of well paid programmers... supported by the Bill & Melinda Gates Foundation (as they deserve!)
I use Hawkes Learning Systems for math... VERY good stuff and cheaper than a standard text book (and comes WITH the text book should they like it as well as the e-text.)