In most Dutch classrooms draught results in insufficient ventilation and poor air quality during the heating season, adversely affecting the well being and performance of pupils. Also a considerable part of the year the risk of overheating is high due to the high internal heat load. New analyses show that over 85% of time the heat load and not minimum indoor air quality is the determining factor for the required amount of ventilation. That is if passive cooling is to be preferred above mechanical cooling, with regard to energy conservation. This finding has been added in the latest Dutch guidelines for school ventilation. Because high flow rates are desired without preheating, new draught free air distribution concepts are required. This paper describes the development of such a new concept. Fresh air is supplied through small perforations, scattered over the whole ceiling surface. During the heating season two pilot studies were held to evaluate the practical implementation of the concept in existing schools. To show the application in different existing schools also two design studies are described. The results show that with modest investment costs, extremely low fan energy consumption and a low noise level the indoor environment in classrooms may be improved considerably.