With regard to recently emerged problems of smartphone addiction among adults and adolescents, this paper researched upper-grade elementary students depending on various demographic factors that have not been studied thoroughly so far. The survey was conducted on 1570 students in grades 4~6 of schools in Gyeonggi province. Results showed that, first, the average rate of smartphone ownership was about 66%. Second, about 1% of the students belonged to high-risk group, 5.7% to at-risk group, and normal user group was 93.3%. Third, based on the demographic factors, grade and academic achievements each was significantly correlated to the type of addiction group. For example, students with poor academic performance or in higher grade were more likely to be highly addictive. Fourth, both groups of at-risk and of normal-user pertaining to these factors - in urban areas, male students, sixth-grade, in dual income families - showed higher addictiveness score. But they were contrasted in the aspects of household economy and academic performance: at-risk group was more addictive in affluent families or excellent academic performance, whereas normal-user group had higher level of addictiveness in case of poor families or lower academic performance.