A key theme in the science education literature concerns the reluctance of students to participate in Science, Technology, Engineering, and Mathematics (STEM). Self-determination theory (SDT) states that social factors in an educational setting, such as teachers’ motivating style, can influence students’ motivation and engagement. This paper investigates the relationship between STEM teachers’ motivating style (autonomy support, provision of structure, involvement) and students’ motivation and engagement with regard to STEM. Furthermore, the relationship between students’ motivation and students’ engagement is investigated. Thirty classroom observations were conducted in different STEM lessons, to assess teachers’ motivating style and students’ engagement. The students’ motivation was assessed at the end of the school year, using an online questionnaire. The results reveal that STEM teachers’ provision of structure is positively linked to students’ motivation and engagement with regard to STEM subjects. The impact of teachers’ autonomy support was negatively predictive for students’ autonomous motivation, and positively predictive for students’ engagement. A negative relationship between students’ controlled motivation and engagement was found. Based on these results, this study suggests that taking teachers’ motivating style into account in future educational initiatives regarding STEM is highly relevant as a means of stimulating students’ motivation and engagement.