Teaching has often been discussed as skills hence teacher education is focused on promoting a certain set of competencies. The changing view of education has turned researchers to study the internal factor of teachers to account for teaching behavior that benefits learners. The current study is underpinned by self-determination theory (Ryan & Deci, 2000). It aims to identify work engagement as a significant factor that affect teachers to adopt teaching behavior that effectively supports learners, it also explores teachers social support behavior. It is a mixed method study including an investigation based on psychological measurement and a qualitative study based on interview. The paper first reports a survey study which is based on 309 Hong Kong junior secondary school teachers. The path analysis results showed that Work Engagement fully mediates the impact of Autonomy and Competence, as two factors of Psychological Need Satisfaction at Work, on teachers' Social Support giving. It then reports an interview study on twenty teachers as the second part study. The content analysis results suggest that social support is featured by teachers' use of questioning, dialogical feedback, authentic interaction, and metacogntive teaching in the classroom. Enabling learners to pursue a good life are identified as a common goal of teaching. The study provides a theoretical framework to explain teachers' engagement behavior. It contributes an important perspective that effective teaching and teaching competencies should be generated internally, suggesting that basic need satisfaction should be promoted as it support teacher development and student learning positively. The study also has important implications to make on teacher education and training. Copyright © 2022 RPIC.