The purpose of this study was to investigate the effect of lessons conducted in out-of-school learning settings on 5th graders science achievement within the scope of a guidance material that was prepared to be used in out-of-school learning settings in accordance with the "Let's Solve the Riddle of Our Body" chapter objectives. The pretest/posttest equalized control group design, which is one of the quasi-experimental designs, was used in this study. The sample of this study was composed of a total of 31 5th grade students (15 were in experimental group, 16 were in control group) that were selected from secondary schools in the first semester of the 2015-2016 academic year in Tokat Province. Let's Solve the Riddle of Our Body Chapter Achievement Test (LeSROBAT) was administered before and after the implementation of the guidance material to measure the students' achievements and retention. The lessons were conducted as suggested by the current curriculum in the control group. The data were analyzed using independent samples t-test and covariance analysis (ANCOVA). As a result of the analyses, it was found that the LeSROBAT post-test scores of experimental group were significantly higher than the control group. Within this context, it was concluded that the out-of-school learning settings positively contributed to academic achievement and the guidance material that was developed within the scope of this study was effective. The results of retention test analyses did not reveal any significant difference between the posttest and retention test scores of experimental and control groups. When the LeSROBAT retention test scores were examined, it was observed that the scores of experimental group was higher than the control group.