This research analyzes the effect of the implementation of citizen science activities in the Environmental Education (EE) subject program of the Degree in Primary Education applying Experiential Learning Theory. Environmental Attitudes Inventory (EAI) was used to measure the change in environmental attitudes (EA) of 173 preservice teachers through a pre-test--post-test experimental design without a control group. Participation in the training program significantly improved EA in the 12 dimensions defined in the EAI. Of the dimensions included in the second order factor "Preservation," "Enjoyment of nature" reached the largest effect size and "Environmental movement activism" is the one that obtains the smallest effect size. With regard to "Utilization," all dimensions presented a large effect size. No significant differences were found in EA based on the gender variable. It can be concluded that the incorporation of citizen science activities in the EE program significantly improves EA.