This article investigates how the secondary education expansion policy shapes the construction of teacher efficacy. Bandura's self-efficacy theory underlies this article, and qualitative case study was the main approach. Around 12 and 16 teachers, respectively, participated in individual and group interviews. Findings indicate that the inadequate implementation of the policy affected the sources of teacher efficacy. The study identified that social persuasion is one of the most social self-efficacy contributors. It also pointed out factors which support a view of mastery experience as the most powerful source of self-efficacy, and the causes of teachers' negative emotional states beyond school context.