Despite its abstract nature, mathematics is an indispensable tool in solving real-life problems. In developing and changing world, social needs have also changed, which directly impacts education. Real-life problems are problems that require the use of several abilities and disciplines, unlike the uniform problems used in traditional education. Several methods and techniques are used to solve these problems. Among these methods, STEM is frequently used in solving real-world problems. STEM education is an approach that aims to teach science, technology, engineering, and mathematics disciplines through real-life scenarios. This study aimed to use mathematics in real-life problems and STEM was decided as the most suitable method. The participants of the study involved 11th-grade students in a Vocational and Technical Anatolian High School located in a rural district of a city. Observation notes, focus group interviews, student artifacts were used as data collection tools. In the first semester of the 2018-2019 academic year, an action plan including STEM focused instructional processes were implemented following the basic mathematics curriculum standards, and the data was collected by the researcher in the light of the action plan. The findings revealed that the students’ knowledge and skills in mathematics were positively influenced, as well as in other STEM areas. Knowledge and skills were positively affected by the students' attitudes towards mathematics. Student skills were shifted to higher levels, their traditional view patterns of mathematics changed and they became more eager to learn and to actively participate in the mathematics lessons.