Schools are planning to re-open in September and with the recent increased awareness of airborne transmission of Covid-19, there is an urgent need to monitor the situation and to provide guidance on ventilation best practice. This is emphasised by the expected onset of cooler weather when there will be a conflict between maintaining high fresh air ventilation flows and energy consumption and occupant comfort. We will quantify the risk of airborne COVID-19 transmission in schools and evaluate the effectiveness of mitigation measures, by developing techniques to assess the absolute risk of infection in a given indoor space, using field studies in primary and secondary schools, complemented by laboratory experiments and CFD to elucidate the flow patterns responsible for airborne transport. The understanding generated will underpin recent developments in infection modelling to predict the likelihood of airborne transmission within schools. The project will reduce the uncertainties associated with airborne transmission routes and provide evidence to evaluate mitigation measures. The scenarios we will investigate include changes to ventilation, use of screens, classroom lay-out and occupancy profiles. The methodology will facilitate application to offices, restaurants, shops etc. Airborne infection occurs through re-breathed air, the concentration of which can be directly inferred from measurements of CO2. Indoor flow is strongly affected by the locations of windows or vents, the heat rising from occupants/equipment and disturbances caused by people movement. Thus, accurate representations of these processes in the laboratory and CFD are needed to interpret the monitoring data currently collected in schools, which are typically single point measurements.