In this research, the effects of STEM (Science-Technology-Mathematics-Engineering) activities on academic achievement of prospective teachers were researched, their opinions on STEM activities were sought. The research was based on a semi-experimental model with pre-test and post-test control group. During the application phase, the topic of Work-Energy subject was taught through STEM based 5E model in the experimental group, while in the control group, the lessons were conducted using traditional teacher centred teaching. The research group is comprised of second-year students in Elementary Mathematics Education taking Physics I course at the Dokuz Eylul University in Turkey. A statistically significant difference was found in favour of the experimental group in terms of prospective teachers' academic achievement. In addition, the positive opinions of the prospective teachers from the experimental group on STEM activities were that STEM activities included encouraging group work, assisting students to produce original work, enabling them to do research, and ensuring that the information learned is permanent. The negative opinions of them on STEM activities were insufficient time for the application, the dominance of some students during the group work, and difficulties with noise levels in class.