Quest for knowledge is universal...
Yes, a teacher would be a handy thing, but that requires a person to be present and willing and able, probably hard to find in Ethiopia... for free, anyhow. Give these kids an internet connection (probably not part of the experiment) and the world is their oyster. I gave up classical learning in college, because it doesn't work for somebody who wants to learn at a faster pace than what's available. Sure these kids will probably play more games than not, but eventually they will ask questions of things they're interested, the tablets could provide them with that. I learned EVERYTHING about my current career (videography / video editing) on the internet! (Not through courses, but through forums, tutorials, etc.) I get paid well to do what I do. The general public was my teacher, and can be theirs too!
Teachers DEFINITELY have their place, but if Ethiopia was that place, they'd be there and this experiment wouldn't be necessary...