Socially desirable responses have been widely discussed as potentially biasing self-reported measures of environmental attitude and behaviour assessment. The direct and moderating effect of social desirability on children has not been analysed before. By applying a Lie scale together with a two-factor environmental attitude set measure and a scale of self-reported General Ecological Behaviour (GEB) to 198 pupils, we found a moderate impact of Lie scores on only one of both attitude measures and a small impact on GEB. In a multiple regression analysis general behaviour was predicted by attitude, social desirability, and the interaction of both. Social desirability had no moderating effect on the relationship between environmental attitudes and behaviour. Implications of these outcomes for research on environmental issues with children are discussed.