Although many studies are analyzing the effect of the STEM model on students' cognitive characteristics, it is known that there are not many studies conducted especially on its impact on students' conceptions of learning (COL), and it is thought that there is a need for these studies as well. It is necessary to determine how COL, which may vary depending on cultural features and learning environments, will take shape with STEM, a learning model of great importance. Therefore, in the current study, the effects on Turkish high school students' academic performances and conceptions of learning biology (COLB) in STEM activity enriched biology courses were investigated. This study implemented a true-experimental design, which was carried out with 99 high school students. COLB Scale was used to determine the students' COLB, and Nervous System Achievement Test (NSAT) was used to assess their achievement regarding the nervous system's structure, function, and mechanism. The data analysis was conducted with MANOVA. According to the analysis results, the STEM activity enriched learning model affected the students' academic performances; however, it made no difference in terms of their COLB. [This study was orally presented at the Second National Biology Education Congress.]