The aim of this study was three-fold: (1) to determine 6th, 8th and 10th grade students' environmental knowledge and attitudes in Turkey; (2) to investigate the effect of the grade level and gender on students' environmental knowledge and attitudes; (3) to explore how environmentally responsible behaviour is related to environmental knowledge, affects, behavioural intentions, and demographic variables. Data were obtained by the administration of the Turkish version of Children's Environmental Attitudes and Knowledge Scale to 1,977 students from 22 randomly selected schools located in urban areas. The data were analysed using one-way analyses of variance, independent samples t-test, and multiple regression analysis. A statistically significant effect of grade level was found on environmental knowledge and attitudes. While the effect of gender on attitudes toward the environment was statistically significant in favour of females, the gender difference on environmental knowledge was not statistically significant. Multiple regression analysis revealed that environmentally responsible behaviour can be predicted by behavioural intentions, environmental affects, gender, and age. Environmental knowledge appeared to be influential on behaviours not directly, but mediated by behavioural intentions and environmental affects. (Contains 4 tables and 2 figures.)