In a previous lifetime I used to be a professional instructor. I taught advanced programming and design in both an academic and an industry setting, and created a very nice set of lesson plans. Towards the end of my teaching phase, I lamented the fact that when I stopped teaching, my experience would essentially vanish and be wasted. Fortunately I was able to secure a book publishing contract and capture my knowledge of one subject - UNIX - as a successful book from Prentice Hall.
My experience, however, was a rare case. The wisdom and knowledge of most good teachers is usually passed on to a relatively small number of students. This is of course very inefficient; there should be a way to capture the best teaching practices and make them freely available to anyone who wants to learn. I call this "amplified teaching" because it amplifies the education impact that a single teacher can have on the world's population.
In some respects, this is what books are meant to be. However, books aren't free and books don't interact with students. If a student gets stuck on a particular point, it requires human intervention. We should be able to automatically handle many common student questions so that teachers can focus on the more subtle points or on inventing new fun projects.
I firmly believe that 50%+ of what teachers currently do can be captured and reproduced using computer systems. Does this mean that teachers will no longer be necessary? Not at all. What it means, however, is that the responsibility of teachers will shift from teaching the basics using traditional means to facilitating more advanced approaches like project-based learning. This is a win-win situation. Students will be able to learn the basics at their own pace in a personalized manner, and teachers will be able to contribute at a higher level than they're currently used to.