Hitzefrei, heat-free, means that school ends early because it is too hot. There is no national rule, and the head teacher decides. Several states set guide values in advance. In Baden-Württemberg, the value is 25 degrees Celsius in the shade at 11 a.m., and lessons end at the earliest after the fourth period. It does not apply to the upper years of the Gymnasium or to vocational schools. In North Rhine-Westphalia, the value is more than 27 degrees in the classroom, and not if it is below 25 degrees outside. Primary schools must supervise the children even when lessons are canceled. Mecklenburg-Western Pomerania states plainly that there is kein Recht auf Hitzefrei, no right to heat-free.