Shifting from teacher-centred to student-centred practices requires teachers to understand strategies to interact with students in science classes. Formative assessment strategies are very critical component of classroom interaction where teachers obtain information about student learning wherever possible. Traditionally, however, teachers ask questions and evaluate student responses but without investigating student contributions to the classroom interaction. This qualitative study aimed at developing teachers’ knowledge of formative assessment strategies when teaching science-based inquiry in Saudi Arabia. 12 teachers were observed when teaching science and details of one teachers’ practices of formative assessment is presented in this study. Formative assessment framework that describes assessment conversations is used and modified to observe teachers’ assessment practices. Assessment conversation consists of four-step cycles, where the teacher elicits information from students through questioning, the student responds, the teacher recognizes the student’s response, and then uses the information to develop further inquiry. Findings indicate that teachers ask questions and receive responses but rarely allow students to share their own ideas or discuss their own thinking. The study underlines the importance of integrating formative assessment strategies during scientific inquiry teaching for professional development as a way to increase student participation and allow opportunities for students’ inquiry in science classes.