I think there are two things to consider here. One is the use for whole class testing/polling which I think makes pretty good sense - there is plenty of published data suggesting that personal response systems (clickers), for example, enhance student learning.
No, the real issue here is whether or not student use of these devices during lecture enhances or detracts and whether it enhances learning when used to research in-class assignments. This is the real question.
It seems to me that their use during lecture will diminish student learning because students cannot multitask. However,this point is probably moot because there should be less lecturing and more active learning going on in the 21st century classroom. I think students will be less inclined to send texts and check email if they are actively engaged in the class. If the technology is used to complete in-class assignments as can happen, for example, during the application phase of Team-Based Learning then I think this is similar to Eric Mazur's assertion that if it is an authentic assessment (formative like TBL apps or summative as in a final exam) it should make no difference. If the question or problem being considered by the student is directly searchable by Google, then it probably isn't an authentic assessment. Which means that this is a difficult task for instructors: setting authentic assessments.
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