The purpose of the study is to investigate the effects of an applied environmental education project carried out using the green-class model on students' environmental knowledge and its retention. 101 7th grade students attending Nazim Akcan Primary School in the Altindag Province of Ankara participated in the study. The study was carried out in the form of pre-test post-test monitoring design. The Environmental Knowledge Test was used as a data collection instrument. For the analysis of the data, a two-way ANOVA for mixed measures was used. The post-test and monitoring test means of both the experimental groups were found to be significantly higher than the control group. As a conclusion, the green-class model considerably enhanced the environmental knowledge of the students and its retention. It was able to make a great contribution to the environmental knowledge of the students residing in a low socio-economic neighborhood. This project is an original study and can be implemented with different samplings. (Contains 6 tables and 1 figure.)