Considering the serious environmental threats facing Egypt, environmental education (EE) that provides the knowledge, skills, and motivation to take individual or collective action is needed to create a sustainable quality of life. This study was carried out aiming at measuring the level of environmental knowledge among preparatory school students in Alexandria, determining their attitudes towards some environmental concepts, and assessing the effect of EE on these knowledge and attitudes. The study sample was selected by stratified random method, and the assessment was conducted using a questionnaire. Results of the study revealed that 77% of the students had poor level of environmental knowledge and that 23% had fair level. In addition, 80% of the students were found to have negative attitude toward the environment and the remainder 20% were indifferent. Such knowledge and attitudes were positively correlated to their socio-economic levels. Following six EE sessions, an improvement in their knowledge and attitudes was observed where 69% of the students had a satisfactory level of knowledge and 88% had positive attitude toward the environment. Attitude was found to be positively correlated to their level of knowledge prior to and following the EE sessions. These results support the need for development and implementation of environmental education programs as part of the regular school curriculum.