The purpose of this study is to examine teachers' beliefs concerning the effects on students using mobile devices, and to determine whether these beliefs vary according to the demographic characteristics and Internet usage purposes. For this purpose, a demographic information questionnaire and the scale developed by Diker Coskun & Kizilkaya Cumaoglu (2013) were revised with validity and reliability studies and utilized on teachers (N = 200). In total, the scale has three dimensions (with a total of 15 items). These are social effects (9 items), psychological effects (3 items), and learning-related effects (3 items). According to the results of the study, teachers believe that students are affected by mobile devices on all three dimensions of the scale (social, psychological, and learning dimensions). The most striking finding of the study is related to the learning dimension of the beliefs concerning mobile devices scale. In every Internet usage purpose examined within the study, it was determined that the teachers' beliefs concerning the "learning" dimension are always more positive than those that do not use the Internet for any given purpose.