Universal Design for Learning (UDL) is a framework for instruction enabling instructors to impact learners with varying cognitive strengths and skills by emphasizing the need for multiple means of representation, expression and engagement. UDL is increasingly used in many post-secondary programs; however, this framework is relatively unknown to STEM instructors. Research focusing on UDL in post-secondary has primarily centered on teacher and student perspectives. This project uses observations to describe the extent to which student-centered active learning STEM courses implemented UDL practices. Observations were conducted during introductory physics SCALE-UP and chemistry inquiry laboratory courses using a protocol based on the UDL framework. Observers coded the prevalence of 31 practices in four categories: introducing and framing new material; content representation and delivery; expression of understanding; and activity and student engagement. These observations allowed researchers to identify specific areas of needed improvement and will be used to facilitate STEM instructors incorporation of UDL in future lessons.