Study of students' knowledge about air pollution can help authorities to have better imagination of this critical environmental problem. This research examines guidance school and high school students' ideas about air pollution and the results may be useful for the respective authorities to improve cultural and educational aspects of next generation. In this cross-sectional study, a closed questionnaire was used to examine knowledge and ideas of 2140 randomly selected school students of Tehran-Iran about composition of unpolluted air, air pollution and its causes and consequences. Cognitive scores were also calculated. Outcomes were compared with results of similar researches in Australia, Hong Kong and the United Kingdom. While a student's 'cognitive score' could range from -16 to +16, Iranian students' mean cognitive score was equal to +2.97. There was not significant statistical difference between girls and boys (P=0.32). In response to question "most common gas in unpolluted air" nitrogen was mentioned by only 23.7%, While 45.1% of students mentioned oxygen. In general, student's knowledge was not acceptable and there were some misconceptions such as "supposing oxygen as the most prevalent gas in unpolluted air". The findings of this survey indicate that, this important stratum of society of Iran have been received no sufficient and efficient education and sensitization on this matter.