In this dissertation, I investigate how the ongoing proliferation of one-to-one computing shapes science teaching and learning within urban secondary school classrooms. The relationship between teachers and students is increasingly mediated by digital platforms sold by commercial companies, which have seldom been systematically investigated within classroom-based research in the U.S. To investigate how these platforms shape teachers’ instructional practice, I partnered with reform-oriented science teachers in a large, urban district. With these teachers, I developed multimodal classroom observation methods that pair video of the physical classrooms with screen capture of teachers’ laptop screens as they teach. Using these data, across three articles I describe how teachers and students juggle a multitude of digital tasks, surfacing how the digital interactions that are hidden from view shape the instruction that unfolds. In the first article, I illustrate the ways instruction is frequently influenced and interrupted by teachers’ need to feed data into platforms to communicate with administrators and parents—a burden that falls most severely on teachers of the most marginalized students. In the second article, I focus on teachers’ experiences with two platforms that attempt to ease their workload through automation. Their experiences problematize claims that increased automation saves instructional time or increases teachers’ relational bandwidth to be present for students. In the last article, I focus on students’ dialogue and sociality with one another in small group work, highlighting how students’ individualistic interactions with school-issued computers may inhibit the more rigorous, collective knowledge construction upheld in the science education literature. Across these articles, I contribute an expanded toolkit for how we view and understand what happens when teachers integrate technology into their instruction—making visible the often invisible consequences of digital mediation in everyday classrooms.