According to the OLPC wiki
the concept is more than simply giving computers to children "to somehow make them learn more." Instead they write: "While the technical aspects create a platform for change, the real benefits will come from improved educational practice enabled by immersive access to connected laptops." So, no claim that simply giving children laptops lets schools off the hook.
The OLPC advances an idea (to me somewhat orthogonal to basic educational practice) that connecting laptops connects the students
together in ways that gives rise to other beneficial effects. Since we're all sitting here reading Slashdot it's an easy analogy -- Slashdot creates a community with a shared common interest, but with diverse opinions on those interests, and at the end of the day it's that diversity that is of interest. We read to learn what others think. So OLPC (ought to) create a means for children to interact with other children with the same effect, but on many other topics besides "news for nerds." And that sounds like a fine idea to me.