Excessive use of mobile phones causes students to fare poorly in elementary, junior high and high school, not only because it makes them lose their concentration due to a lack of sleep, but also because it apparently compromises what they have studied, researchers say.

Students who spend several hours each day staring into mobile phones or smartphones tend to change their sleeping habits and stay up late to use the devices, education ministry research published Thursday showed.

The research was conducted last November with 23,139 participants from the fifth grade of primary school up to the third year of high school, at 771 public schools nationwide.