Inquiry-based teaching and learning methods are more and more widely used in the teaching natural sciences all over the world. The elements of inquiry are included in many national sciences' core curricula and indicate that students should be actively involved in acquiring knowledge. This fact changes the teacher's role in the classroom and the structure of everyday lessons. Independent inquiry helps students to develop various elements of scientific education, gain specific skills and competencies. Consequently, the assessment methods used so far are no longer sufficient and they should be expanded with new strategies, tools, and criteria. In recent years, there were many projects, in which teachers were trained in using both inquiry-based instructions and formative assessment. So far, unfortunately, there has been limited information on how teachers bring theory into practice and combine the new teaching and assessment methods, and how they adopt available teaching materials during everyday classes. This case study explored how experienced chemistry teachers, who have broad content, pedagogical content, and inquiry methodology knowledge, integrate inquiry-based teaching with formative assessment for the first time. The results of the study revealed the main limiting factors and teachers' dilemmas.