Students' opportunities to learn how to think are embedded in the instructional tasks with which they are invited to engage in the classroom. Prior research has revealed that the selection and use of cognitively demanding tasks does not guarantee high-level student thinking during their enactment. To address this challenge, we designed and implemented a professional development (PD) in which participants analyzed video clips of the enactment of cognitively demanding science tasks. Using transcripts of pre-and post-PD interviews during which participants were asked to respond to specially selected video clips, we analyzed what the participants attended to and how they made sense of what they saw. The findings suggested a change in terms of a growing tendency to attend to teaching as constituted in the interaction of the teacher, students, and task and to adopt an interpretive stance while talking about what was seen in the video clip.