Cleaning of room air from particulate contaminants was performed using electrostatic air cleaners (precipitators) in four classrooms of 12-year old pupils. The air cleaners were active/inactive according to a cross-over design for 2 + 3 weeks during pollen season. Health questionnaires and cognitive tests were used to investigate the impact of air cleaning on perceived health and on cognitive skills that relate to schoolwork and learning (semantic and episodic memory, logical reasoning, attention, reading comprehension). Pupils stating themselves as being sensitive to airborne particulate contaminants, such as pollen and pet allergens, experienced somewhat less irritation in airways and eyes when the air cleaners were active (p=0.02). The most sensitive pupils also scored about 25% higher on the cognitive test relating to semantic memory when the air cleaners were active (p=0.015). No significant effects were however found for the four other cognitive skills.