Laptops are commonplace in university classrooms. In light of cognitive psychology theory on costs associated with multitasking, we examined the effects of in-class laptop use on student learning in a simulated classroom. We found that participants who multitasked on a laptop during a lecture scored lower on a test compared to those who did not multitask, and participants who were in direct view of a multitasking peer scored lower on a test compared to those who were not. The results demonstrate that multitasking on a laptop poses a significant distraction to both users and fellow students and can be detrimental to comprehension of lecture content. ► We examined the detrimental effects of laptop multitasking on classroom learning. ► Learners who multitasked during class had reduced comprehension of lecture material. ► Learners in-view of multitaskers also had reduced comprehension of lecture material. ► Multitasking or being seated around multitaskers impedes classroom learning.