I've seen lots of studies saying exactly that. I've also seen some that say the have no effect. Most of the studies that say they are helping say they increase student engagement which normally helps with attendance and test scores. As far as IT staff. Chromebooks are easy, they are all managed centrally from a website. iPads aren't bad and can be manged through special software centrally. The biggest problem is its a lot more devices with the same number of people or less.