I'm looking for statistics about the US and/or world digital education
content market - i.e. web-based teaching materials used in schools
and/or colleges/universities.

Specifically, I need recent (2004 or 2005) figures for the US and/or
world market size. If you can only find the percentage of educational
teaching materials in digital (as opposed to print) form, I can derive
the market size.

Ideally I'd also like future projections for the market size, and the
current growth rate of this digital market (which I can of course
derive if you find data for successive years).