Many researchers assert educators must develop a shared instructional vision in order for schools to be effective. While this research tends to focus on educators' alignment around goals of science classrooms, I argue that we can't assume that educators agree on what they see when they look at science classrooms. In this dissertation, I explore the variability in what teachers and leaders notice in science classroom episodes and how they reason about what they notice. I ground my studies in real classroom practice: a videotaped lesson in the first study and a live classroom observation in the second. In Chapter 2, I discuss the importance of grounding discussions about teaching and learning in classroom artifacts, a commitment that motivates my dissertation: educators may have a shared vision when discussing teaching and learning in the abstract but disagree about whether that vision is being realized in a classroom. I then describe and analyze the video clip I used in my interviews, highlighting moments that I consider to be good teaching and learning. In Chapter 3, I present my first study, in which I showed this episode to 15 different science teachers, science instructional leaders, and principals. I found that participants attended to many different features in the episode, which led to significant disagreement about what is happening in the episode. Additionally, I found that these differences in attention corresponded to differences in how participants were framing the activity of watching the clip. In Chapter 4, I explore the attentional variability of one science instructional leader, Valerie, in multiple contexts. In addition to interviewing Valerie about the videotaped lesson, I also observed Valerie engage in an "observation cycle" with a teacher. Even though Valerie is quite skilled at attending to student thinking in some contexts, I found that Valerie's attention is strongly context-dependent and gets pulled away from students' scientific thinking when she uses a district mandated form. Finally, in Chapter 5 I summarize my findings and describe the implications my work has for both research and practice.