Science educators regard long-term investigations as one impactful form of teaching science through inquiry in K-12 classrooms. While we have idealized notions of what this work looks like, we have few, if any, descriptive studies about investigations that engage students in sustained, focused work over a period of time longer than a few days or even weeks. In a policy context that calls for teachers to develop strategies for engaging students in authentic science practices, such as those that can come from long-term science investigations, we would do well to learn from experienced teachers. This study followed three middle school science teachers in a large U. S. urban school district as they conducted long-term investigations. Using discourse analysis and taking a sociocultural perspective, this study documented the classroom talk and interaction of teachers and their students. The study's goals were to describe how teachers engage students in long-term investigations and the ways that classroom interaction involved specific reform-based science practices. Data include field notes and transcripts of audio recordings from 15 observations of three experienced middle school science teachers, three semi-structured interviews with each teacher, curriculum materials, student work, and classroom demographic data. Teachers engaged students in whole group, small group, and one-on-one conversations about several stages of the long-term investigations. Teachers most often discussed two of the eight science practices: 1) planning and carrying out investigations; and 2) obtaining, evaluating, and communicating information. The planning discussions involved conversations about identifying and describing variables, measuring and recording data, and concerns about data collection procedures. Conversations about using and communicating scientific information included talk about formal science writing conventions, and using background information to support all other parts of the investigation process. In all of the observed lessons, regardless of the practice or types of investigations students were to engage, teachers used curricular tools to support students' work, scaffolding students' introduction to and use of scientific content, practices, and discourse. In these ways, teachers helped students master a science-specific vocabulary and set of practices that allow for the authentic exploration of science concepts. This study describes how teachers who generate opportunities for students to experience two science practices more often than others, which may have implications for science education and science education research--especially concerning how science practices are engaged in classrooms - moving forward. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]