The current study investigates the effects of outdoor classrooms on the third-grade male students learning in science lessons. A pre-test and post-test quasi-experimental field research are conducted using experimental and control groups. A study sample of 54 male students at a school in Shiraz was selected by the non-random multi-staged sampling method. Exams developed by the researchers were taken from both groups of students on two occasions, before and after they received nine consecutive science lessons within their respective learning environments. The results evaluated by Multivariate Covariance Analysis (MANCOVA) revealed that students' exam performance in open space increases up to 17.36%, 20.72%, and 21.15% for 'advanced,' 'proficient,' and 'below basic' students, respectively. There is a meaningful relationship between having classes in an open space and students' exam scores. This relationship depends on their performance and complexity and comprehension of the question levels.