This article examines the effect of different educational approaches to environmental education (EE) in the environmental attitudes of 507 preservice teachers. In one experimental group EE was addressed in a science subject and in other experimental group in a literature subject. The latter integrated content and competences in a transdisciplinary way, overcoming the idea that environmental attitudes should only be addressed in science classes. The analysis of their responses to the Environmental Attitudes Inventory (EAI) in a prestest-postest design show that both approaches were able to increase their pro-environmental attitudes, while the control group showed no significant changes. The educational intervention at the literature subject was able to significantly increase those dimensions related to preserving nature and the diversity of natural species in their original natural state, while the educational intervention at the science subject was also able to significantly decrease those dimensions related to the belief that it is right and even necessary to use and alter nature, natural phenomena, and species for human objectives. Female future teachers had more favorable attitudes towards nature than their male counterparts, but no statistically significant differences were observed according to gender for a specific educational approach.