This constructivist study investigates 225 student drawings and explanations from three different schools in the midwest in the US, to identify seventh grade students' mental models of the greenhouse effect. Five distinct mental models were derived from an inductive analysis of the content of the students' drawings and explanations: Model 1, a "greenhouse" for growing plants; Model 2, greenhouse gases cause ozone depletion or formation, causing the Earth to warm; Model 3, greenhouse gases, but no heating mechanism, simply gases in the atmosphere; Model 4, greenhouse gases "trap" the sun's rays, heating the Earth; and Model 5, the sun's rays are "bounced" or reflected back and forth between the Earth's surface and greenhouse gases, heating the Earth. Science textbooks are critiqued in light of the students' mental models and curricular and instructional implications are explored. (Contains 3 notes, 3 tables, and 5 figures.)