The study will include three sessions in total (all taking place at schools): (1) screening session, (2) baseline session and (3) post-intervention testing session. Children will also be asked to wear an actigraphy device for 5 consecutive nights before and after the treatment. In addition, children will be asked to give saliva samples on a few occasions (both at home - pre- and post-intervention -, as well as during the baseline and testing session visits).