The understanding of pupils in schools in England between the ages of 11 and 16 about air and air pollution has been studied using a closed-form questionnaire with over a thousand students. Items for the questionnaire were derived from the results of an earlier open-form questionnaire completed by a smaller number of students. The ideas explored included the composition of unpolluted air, the nature of air pollution, its biological and environmental consequences and what might be done to reduce it. There was a degree of uncertainty in students' minds as to what exactly constitutes unpolluted air, though students generally seemed well informed about the consequences of air pollution. Along with their cognitive understanding, the questionnaire explored students' views about what they and others could and should do to reduce air pollution. In this they seemed agreed, amongst other things, that financial penalties were less acceptable than legal compulsion. Cluster Analysis was used to probe further, and revealed a number of distinct groups of students, each assuming different positions of understanding and desire for action. A comparison of these cognitive and affective variables revealed relationships which raise important implications for teaching.