I doubt that studies will find improved outcomes. Or rather, initial studies *will* but over time the effect will diminish as a wider swath of teachers use the technology (any technology). That's my prediction anyway, apply it wherever you will. Quality of instruction will always be more important, though I don't fault teachers at all for investigating new technology and techniques - some uses may well turn out to be worth the effort.

I want to make two points:
1) Instead of likening iPads or other computing platforms to telephones, a better analogy might be to watches. Remember when digital watches first became mainstream (well, *I* do)? For a time it looked like the analog watch was going to be wiped off the face of the earth. But, because analog and digital watches each have areas where they are better than the other, both have survived.

I think that's largely because the dimensionality of an analog clock is different from that of digital - more types information are displayed at a glance. I see the same thing being true of physical textbooks vs digital.

2) Media choice should match the desired time permanence of information. I consider digital information to be more ephemeral than paper books - though of course either can be destroyed. I think digital is a great way to store certain school projects! Not so good for something that I might want to refer back to in 25 years.

I guess elementary school textbooks meet the second point, but I think they fail the first. I love ereaders for certain books - those which are meant to be read sequentially. With textbooks, one tends to move back and forth through the pages, referring to different sections, which is why I don't like digital textbooks.