The present study was aimed at investigating the effects of a video feedback coaching intervention for upper-grade primary school teachers on students' cognitive gains in scientific knowledge. This teaching intervention was designed with the use of inquiry-based learning principles for teachers, such as the empirical cycle and the posing of thought-provoking questions. The intervention was put into practice in 10 upper-grade classrooms. The trajectory comprised four lessons, complemented with two premeasures and two postmeasures. The control condition consisted of 11 upper-grade teachers and their students. The success of the intervention was tested using an established standardized achievement test and situated measures. In this way, by means of premeasure and postmeasure questionnaires and video data, an assessment could be made of the change in students' scientific knowledge before, during, and after the intervention. In this study, we primarily focused on the dynamics of students' real-time expressions of scientific knowledge in the classroom. Important indicators of the effect of the intervention were found. Through focusing on the number of explanations and predictions, a significant increase could be seen in the proportion of students' utterances displaying scientific understanding in the intervention condition. In addition, students in the intervention condition more often reasoned on higher complexity levels than students in the control condition. No effect was found for students' scientific knowledge as measured with a standardized achievement test. Implications for future studies are stressed, as well as the importance of enriching the evaluation of intervention studies by focusing on dynamics in the classroom.