Using an ingenious design, two researchers tested the effect of using an electronic device for non-academic purpose on:
Over the course of the semester, students answered 126 questions in class on just-presented content. Each of these questions was then paired with another question that appeared on both a unit exam and the final exam.
Interestingly, results showed that “dividing attention between an electronic device and the classroom lecture did not reduce comprehension of the lecture as measured by within-class quiz questions. Instead, divided attention reduced long-term retention of the classroom lecture, which impaired subsequent unit exam and final exam performance” (quote from the original article.)
The effect also grew with time, amounting to half a letter grade in conventional scoring systems.
Moreover, “exam performance was significantly worse than the no-device control condition both for students who did and did not use electronic devices during the class.”
In that sense, “when considered in the context of a classroom, allowing students to divide attention between an electronic device for a non-academic purpose and the classroom may also have the social effect of distracting other students who are not trying to divide attention.”
Reference: Glass and Kang (2018), “Dividing attention in the classroom reduces exam performance”, Educational Psychology.