The monitors measure the children's movement and exercise
Scientists at Bristol University are tracking children by satellite to find out how school journeys affect health.
More than 1,000 youngsters are taking part in the two-year study into their physical activity and eating behaviour.
Global Positioning System (GPS) watches and waist monitors are worn to measure their movements to and from school.
Researchers said initial findings showed that boys were more active than girls and children became less active when they moved to secondary school.
Project leader Dr Ashley Cooper said: "Some preliminary data we have shows that the children who travel to school by foot or by bicycle are much more active children after school."
The study is part of the university's PEACH project, to investigate the influence of physical activity and eating behaviour in children, with a view to disease prevention.
It is funded by the government, together with cancer research and heart disease charities.