For me, for _typing_, anything less than a good solid desk and a proper keyboard with springs in (i.e. Model M or similar) is already inadequate, the chromebook keyboards I have seen look awful, and probably are given that the whole machine is less than twice the price of a proper keyboard (and probably about the same weight). Yes, the clamshell format is better for typing than a tablet, but both are a lot worse than a desktop. Tablets can also use fancy predictive or modal keyboards (swype et al) to swing the balance back.
Let's also not forget that these are kids, they have not grown up with real keyboards and then switched to touchscreen, they have grown up with touchscreens, they live by their overwhelmingly touchscreen phones, what is more comfortable and efficient for us old ones may not be for them.
> Plus when the lid closes the screen is protected, the iPad has to go into a sleeve of some sort for protection.
The kids' school iPads never come out of the (allegedly mil-spec) protective case, and I'd be a lot happier dropping one than any kind of laptop, closed or open.