A smartphone can be defined as a handheld technology device that is a personal gateway to the world. Statistics surrounding mobile devices continue to break records every year. Currently, 95% of American teenagers own a smartphone device, and smartphone users spend on average about 5.4 hours a day on them. Smartphone ownership, use, and dependency are higher among teens and young adults than any other age group. This study addressed a gap in research by examining high school teachers' perspectives on the impact of smartphone usage on students and classroom smartphone policies. This study contributes to a deeper understanding of how smartphones affect students socially, psychologically, and academically and how teachers' beliefs surrounding smartphones impact the classroom smartphone policies they set. This quantitative study was conducted at five public high schools and one private high school across three school districts located in Southern California. Participants were 248 high school teachers. Results of this study indicate positive correlations among teachers' beliefs concerning the social, psychological, and learning effects of smartphone devices, meaning that all three factors are connected. Results also indicate that teachers who have stronger negative beliefs concerning how smartphones affect students socially, psychologically, and academically typically set a stricter classroom smartphone policy. Additional results reveal significant trends in how teachers at each school district select classroom smartphone policies. The school districts' performance, demographics, and school-wide smartphone policy impact these trends. Implications of this study include helping students regulate their smartphone usage so that they can effectively use it when it is appropriate for learning and put it away when it is a distraction to their learning. Additionally, an increase in face-to-face social interactions among students is needed to increase academic achievement and decrease problematic smartphone use. This study aimed to shed light on the need to create effective and equitable smartphone policies and practices, a one-to-one Chromebook/iPad to student ratio, and access to high-quality internet service to help promote a classroom environment conducive to learning. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]