You need to look at the consequences one at a time.
- If students use e-books they they don't forget their books.
- If the teacher distributes a pdf then the students don't throw it away.
- Many students cannot type fast enough to take notes on an ipad.
- You lose some students to Facebook, but at least the horizontal screen make it easy for the teacher to see what the student is doing.
- The students need access to a real computer if they need to work on a long report or essay in class.
- The students probably need access to a real computer if they need to work with spreadsheets.
- If you install a browser with flash then you can use interactive websites to add variation to the lessons.
I am a high school teacher so some of these points may not ne relevant to young children.