Extensive experimental studies, measurement data, numerical calculations, and practical experience show that window ventilation supported by exhaust fans (i.e. mechanical extract ventilation) is a simple and highly effective measure to increase air quality in classrooms. This approach can be used against the aerosol transmission of SARS-CoV-2 (Helleis et al. 2021a; Lelieveld et al. 2020; Morawska et al. 2021). Mechanical extract ventilation (MEV) is very well suited not only for combating the COVID19 pandemic but also for sustainably ventilating schools in an energy-saving, resource-efficient, and climate-friendly manner (Helleis et al. 2021a, 2021b; Klimach and Helleis 2021) (www.ventilationmainz.de). The ventilation concept presented here is part of a multi-layered risk reduction strategy. As such it is not intended to replace, but rather to complement, other preventive public health measures - including vaccinations, masks and social distancing (Bodenschatz 2021; Cheng et al. 2021; Drewnick et al. 2021; Moriske et al. 2021; P��schl and Witt 2021). After the Covid-19 pandemic, MEV can still be used to maintain high levels of indoor air quality (IAQ) in classrooms, especially in poorly ventilated spaces, lowering the risks from harmful indoor pollutants (McLeod et al. 2021) as well as helping to reduce the spread of seasonal viruses such as colds and flu. 2 Distributed extract ducts or hoods can be flexibly reused, removed and stored, or combined with other devices (e.g. CO2 sensors), which is easy due to the modular concept and low- cost materials.