Background: Young children are part of the most vulnerable segment of the population. They spend a huge part of their lifetime at primary school. Several studies have already been conducted in schools, showing that a poor Indoor Air Quality is linked to a wide range of discomforts and health problems, such as asthma, allergies, lack of focus and decline in cognitive functions. Methods: Concentration of carbon dioxide (CO 2) was assessed in three rooms in a French primary school, with no ventilation system. A Blown Mechanical Ventilation (BMV) was installed in the school and new CO 2 concentration was assessed consecutively, as well as the concentration in fine particle matter with aerodynamic diameter ≤2.5 μm (PM2.5). Results and conclusions: CO 2 concentration was significantly reduced after installing BMV (maximum values measured over a month decreased from 3072ppm to 1500ppm) Moreover, it was demonstrated that BMV prevents outside PM2.5 from entering the classes. The affordable cost and easy installation of BMV are key factors to allow a fast deployment, even in developing countries.