Elementary teachers are expected to teach complex and authentic lessons and integrating multiple disciplines. In so doing, they must take many elements into account, such as disciplinary content, learning standards, and pedagogical knowledge, in an ever more complex environment, including pupils' increasingly heterogeneous characteristics. Our study aims to understand a beginning teacher's classroom activity in the context of a research-training program involving the use of video. The teacher involved was observed giving a science lesson (on buoyancy in a fourth-grade classroom) and then took part in two interviews involving self-confrontation with researchers at 1-week intervals, returning to the classroom between these interviews. Specifically, this article presents a program aimed at training and mentoring a beginning elementary school teacher using video recordings of her classroom activities in Quebec, Canada. The analysis describes the teacher's experience during this training process. In particular, the results indicate that the teacher's participation in this training program changed her concerns related to science education at the elementary level. Her focus shifted from classroom management (e.g., managing hands-on activities in science education and pupils' interactions) to supporting an approach favoring scientific inquiry that truly engages pupils and is anchored in sociotechnical controversies.