Engineering undergraduate programs have become demanding in terms of workload [1]. Along with class time schedules packed with lectures, laboratories, and tutorials, there are a significant number of course assignments that occur outside of class, such as team-based projects and experiential learning tasks [1]. Researchers have encouraged the incorporation of these constructivist approaches into engineering education [2], aiming to help students develop a wide range of abilities (such as complex-problem solving skills and interdisciplinary thinking [3]). However, this increasing number of assignments stresses students [4], [5], negatively affecting their learning results [1], [6]. To understand what students define as a demanding course, several researchers have explored the concepts of academic workload and course difficulty [1], [4]-[7]. So far, there is a growing body of knowledge in Canada and the U.S. regarding factors that affect how first-year students perceive workload [1]. However, little is known about how students perceive course difficulty after dealing with their transition from high school to college, and how the quality of teaching affects their approach to learning [6]. Thus, not only more studies are needed to understand how student-centered approaches could enrich learning experiences from a multi-dimensional perspective [1], [3], [4], but also to examine how these multidimensional approaches make learning more meaningful at a course level [4]. This is particularly relevant in Chile, considering that previous studies have demonstrated that students who major in science and engineering often use surface approaches to learning, focusing on course content that they believe they must memorize to meet assessment requirements [8]. This paper presents a Work-In-Progress (WIP) that is part of a larger study to understand students' perceptions on engineering courses imparted at Pontificia Universidad Catolica de Chile (PUC-Chile). The research question addressed in this paper is: What factors affect students' perceptions on demanding courses in terms of difficulty? To answer this research question, we combined mixed methods with grounded theory research (MM-GT). By MM-GT, we mean the systematic collection and integration of both qualitative and quantitative data toward the goal of theory development [9]. According to recent studies, the MM-GT research approach has become useful to develop and test theory in the fields of education [8], [9]. In this study, we plan to develop theoretical models of difficulty at a course level, following best practices of MM-GT application to provide insights for course curriculum development and teaching reflection in the field of engineering education.