Someone on another post has pointed out the resources on the Khan Academy website. I agree with Alpaca that to have the kids online in lessons would lead to a great deal of distractions. I'm a teacher, and I know that I'd be spending a lot of my time having to deal with kids surfing inappropriate websites (usually pop videos on youtube.com).
However, see this talk by Salman Khan at TED:
I am particularly interested in his idea of 'flipping the classroom'. I.e. Homework is to watch a Khan Academy lecture (or a few), and then lesson time is spent solving problems, rather than the other way round. Therefore allowing teachers more time to deal with each child and making learning more engaging and fun for the kids.
I can really see this flying in the context of the Raspberry Pi and learning to program.