Recent research on scaffolding has turned the spotlight on implementing scaffolding principles for more effective instruction in the classroom. This qualitative study, using observations, investigated scaffolding principles, including continuity, intersubjectivity, contextual support, handover, flow, and contingency, in content-based instruction (CBI) in an international school. To this end, nine hours of science instruction by three science teachers were video-recorded and analysed deductively based on scaffolding principles. The content analysis of observation transcripts showed that continuity, intersubjectivity, and contingency were frequently observed during interaction in science classes, whereas the teachers occasionally implemented contextual support, handover, and flow. The findings revealed that scaffolding principles were mainly related to the conceptual understanding of scientific knowledge and the control of students' frustration in performing demanding activities and understanding complicated concepts. Furthermore, the findings uncovered that scaffolding principles were focused on providing opportunities for students' engagement and genuine communication and eliciting real-life samples and experience through inquiry-based, concept-based, problem-based, and project-based teaching approaches. Most importantly, the teachers frequently employed various scaffolding principles through practical and active participation by doing experiments and projects, modelling, and using video aids for more interactive and collaborative teaching practices. These findings contribute to our understanding of scaffolding principles and teacher-student interaction in science classes.