Interactions in multilingual science classrooms involve local cognitive and sociocultural dimensions along with global contextual aspects such as language-in-education policies. The intersection of these has implications for providing quality science education and supporting diverse students. This study investigates interactions in Lebanese multilingual science classrooms by using an integrative framework to analyze dialogicity of "local" classroom practices, or the extent to which students' ideas are acknowledged and built upon for conceptual learning. Cultural Historical Activity Theory (CHAT) is then used to depict local practices within the larger "global" contextual aspects. Data were collected through instrumental case studies of three middle school science teachers in schools of different socioeconomic levels. Data sources included: (1) videotaped science lessons; (2) teacher and school leader interviews; and (3) student group interviews. Data were then arranged into an activity system for each teacher's classroom. Each activity system showed how local interactions and practices were situated within contextual aspects and the emergent contradictions in each. We discuss what contradictions tell us about interactions in Lebanese multilingual science classrooms and how these can inform professional development in multilingual science education.