It's not uncommon for inexperienced runners to breathe inefficiently or even hold their breath when running. Our breathing activity helps kids remember to breathe during running. It's also a great mental focusing exercise.
The most efficient breathing for runners is belly or diaphragm breathing, where the stomach extends upon the inhale and contracts upon the exhale. Rhythmic breathing is also good. Remind runners to breathe, but don't force a specific breathing method. By discussing breathing and practicing it while standing still, you can help students develop good habits that may translate to their running.