I note that even among those with lower income woning a cell phone is promininet. I am ot sure how high cell phone use is defined, but I would think that hours on the phone would reduce the ability to get the required 60 minutes of physical activity per day, as well as to complete the necessary assignments It could be that those that are less studious any way are the ones that are inclinied to be on the phone rather than completing their school assignments. It would be interesting to note if the ones that are on the cell phone at high rates- eat breakfast every morning, have a balanced meal etc. do they live in neighborhood that facilitates healthy nutritioin and activity( i.e social determinants). Just a quick response.

I am in agreement, look at this;

Kent State University researchers Andrew Lepp, Ph.D., Jacob Barkley, Ph.D., and Aryn Karpinski, Ph.D., all faculty members in the university’s College of Education, Health and Human Services, surveyed more than 500 university students. Daily cell phone use was recorded along with a clinical measure of anxiety and each student’s level of satisfaction with their own life, or in other words happiness. Finally, all participants allowed the researchers to access their official university records in order to retrieve their actual, cumulative college grade point average (GPA). All students surveyed were undergraduate students and were equally distributed by class (freshman, sophomore, junior and senior). In addition, 82 different, self-reported majors were represented.

Results of the analysis showed that cell phone use was negatively related to GPA and positively related to anxiety. Following this, GPA was positively related to happiness while anxiety was negatively related to happiness. Thus, for the population studied, high frequency cell phone users tended to have lower GPA, higher anxiety, and lower satisfaction with life (happiness) relative to their peers who used the cell phone less often.

http://www.kent.edu/news/news-detail.cfm?newsitem=c87da8eb-0e77-dcf2-aad1c317fb742933

I have mixed feelings on this topic. While I find it interesting that those who have higher cell phone usage tend to have lower GPS I think it's more the result of some other underlying latent issue. I don't necessarily believe the cell phone use is causing the issues, more likely the opposite.