The international literature highlights the importance of inclusive education, placing diversity at the core of learning environments. Universal Design for Learning (UDL) is recognized as a framework that promotes accessibility, enabling all students to fully engage based on their abilities through flexible and adaptable learning experiences, serving as a model for fostering a culture of equity, respect and belonging. From this viewpoint, schools are encouraged to prioritize universality and flexibility from the outset of the design process to ensure equal access for all students, while teaching quality is recognized as a key driver of educational improvement. Given this, it is crucial to support the professional development of teachers, emphasizing the development of methodological skills as well as a professional habitus grounded in reflexivity, research, and agency. Rooted in the concept of inclusive education as a transformative practice, this paper focuses on the initial phases of a Teacher Professional Development Research (TPDR) initiative. The study involves a group of in-service teachers applying the UDL approach within lower secondary education. During the launch phase of the TPDR, a qualitative-quantitative tool was administered with two main purposes: first, to assess whether and to what extent the principles and guidelines of the UDL framework were already implicitly present in the participating teachers' daily practices before the training, helping to better orient and contextualize the design of the intervention; second, an ex-post administration of the instrument aimed to compare the data at the end of the process to identify any changes in teaching practices and declared beliefs. The research aims to enhance diversity as an intrinsic quality of educational settings by emphasizing UDL’s role in fostering teaching-learning relationships that promote equity, academic success, and active participation with the objective of assessing whether the TPDR pathway leads to an increase in inclusive practices in the classroom, a positive shift in teachers' perceptions of their professional agency, and a positive impact on students' perceptions of their learner agency. By using a mixed-method approach, it seeks to contribute to the literature on teacher professional development and inclusive education while promoting the co-construction of knowledge within a teachers' community of practice embedded in real- world contexts, driving transformative changes in teaching practices and inclusive processes from an emancipatory perspective. Thus, to focus on the specificity of the context and participants’ needs, teachers were previously asked to state the frequency with which they adopt a set of teaching behaviors that meet the UDL guidelines (27 items, Section 1), and what they think are the potential school barriers to the implementation of the framework (10 items, Section 2), using a quantitative survey, built from existing tools. Within the limits of a self-report tool, the outcomes show that the involved teachers implicitly tend to adhere to UDL principles. In light of the above, we expect that the end of the Teacher Professional Development Action-Research will lead teachers to increase the adoption of inclusive practices focused on the UDL framework as well as a sensible change about their agentic skills, with a positive impact on pupils’ learner agency.