Can you give us some sense of the overall cost? (Not just the $25-35 Raspberry Pi, which alone is just a printed circuit board, but the other components that make it a usable computer for children - monitor, keyboard, mouse, even a case for the RP itself). Cost per usable device (that one student uses at one time) would be ideal, so it's easy to understand how one scales it up. Also, what content do you use besides Khan Academy?
Good question. Breakage rates are extremely low so far (robust and tested tablets that are deployed with low-cost protective cases). In the event of breakage, we've had some fixed in country easily by local vendors who fix basic mobile phones and smartphones - depends on the country. This is based on projects in seven countries now. What makes the Rumie approach different is that after reading all of the research possible to learn everything we can, we get into field ASAP to learn the rest by actually doing and with real data and results to guide rapid product development).