9.15 a.m. standardized snack within the frame of the regular break, 9.45 a.m. to 12.25 p.m. everyday school life, 12.25 p.m. either lunch (control) or only a non-caloric beverage (intervention of 'skipping meal'), 12.45 p.m. to 1.15 p.m. regular lunch break, 1.15 p.m. computerized tests of cognitive functioning, 2 p.m. lunch for the 'skipping meal'-group.