Most New Zealand schools depend on open windows for ventilation. However, classrooms are grossly under-ventilated during cold weather. Consequently, children are exposed to avoidable, high levels of respirable pathogens and pollutants. Conventional mechanical ventilation is prohibitively expensive for schools. An interventional study will investigate the health improvements following installation of a low-cost, solar-heated ventilation system in ten predominantly low-decile junior classrooms (300 children) over two school terms, for two winters. In the first monitoring period, five classrooms will be active (ventilation operational) and five will be a control; control and active groups will switch each term. Streptococci from throat swabs, total airborne bacteria, coughing and sneezing frequency, absenteeism and chemical pollutants will be measured. It is anticipated that increased ventilation will lead to a healthier classroom environment as pathogen levels and subsequent respiratory infections will be reduced, as will chemical pollutants.