The Environmental problem solving model is an instructional strategy to accomplish the aim of environmental education through investigation of environmental problems and issues of the community. This study is intended to compare the instructional effect of the structured model with the unstructured model of environmental problem solving. The experimental group received the structured instruction and the control group received the unstructured instruction. There did not appear to be any significant difference between the groups in regard to knowledge but in regard to knowledge of environmental issues, the experimental group was more effective than the control group. No significant differences existed between the groups in attitude. In regard to investigating skill and evaluation of environmental issues, the experimental group was significantly more effective than the control group. The experimental group was significantly more effective than the control group in regard to environmental action skills. To foster responsible environmental behavior, environmental education a number of methodologies must be considered and learners must be trained to become problem-solving citizens. It was noted that the structured instruction was more effective than the unstructured instruction in middle school where environmental issues were not taught as an independent subject. We conclude that environmental education must be systematically constructed and taught in a manner which takes into account both its goals and the characteristics of the various learners. We conclude that environmental education must be systematically constructed and taught in a manner which takes into account both its internal goals and the situations within which various types of learners explore environmental issues and solutions.