Research indicates that data-informed practice helps teachers change their teaching and promotes teacher professional development (TPD). Although educational data are often collected from digital spaces, in-action evidence from physical spaces is seldom gathered, providing an incomplete view of the classroom reality. Also, most learning analytics tools focus on learners and do not explicitly collect or analyse teaching data. To support teacher-led inquiries in TPD, the authors' Design-Based Research explores the feasibility and effects of teachers actively collecting, with the help of technology, data about their classroom practice and the possible impact of such data on their own teaching. Based on an online survey (N = 94), prior research literature and feedback from teachers (N = 11), the authors demonstrate the feasibility of such data collection and suggest design principles for classroom data-collection tools as, besides usability and ease of use, they also detected interest in customisation, triggering teacher interest and inclusion of teaching data.