 All students from the 15 public middle schools in the city of Larissa in central Greece were invited to measure their weight and height, in order to calculate their Body Mass Index BMI. All the overweight or obese students were invited to take part in the study. The participation was free of charge for the children. Parents were informed about the purposes of the project and were asked to provide written informed consent for participation. The studys protocol was approved by the ethics committee of the Medical Department of the University of Thessaly. 