Inquiry has been an important part of educational theory and practice for the last decades. As in other competence-oriented approaches to teaching and learning, the appropriate support and assessment of the students' competences has been much debated in the context of inquiry-based science education. One way to support and assess students in their learning is formative assessment. The concept is also known as 'assessment for learning' which means that the information on the students' levels of achievement is not used for grading but for planning the next steps in teaching and learning. The use of formative assessment methods as a means of support for students' learning is promoted in national and international position papers and reports. However, in the Swiss teaching practice, formative assessment, particularly formal formative assessment methods which involve a certain degree of pre-definition, planning, and formality, are not widely used nor researched. Therefore, the focus of this study is on exploring possibilities and challenges for the implementation of formal formative assessment methods in the context of inquiry-based science education in Switzerland. The emphasis of the study will be on the teacher perspective.