It is difficult for curriculum reform to achieve sustainable success without support from teachers in the front line. The authors of this paper investigated teacher factors behind the successful implementation of a reformed instructional model, the Dao Jiang Ping (DJP) model, in China. This study is part of a longitudinal project (2012)(2013)(2014)(2015)(2016)(2017) that reported the level of DJP implementation and explored factors that influence teachers' implementation. This paper mainly focuses on the latter. Six teachers were examined to look for reasons behind their different levels of DJP implementation. The theory of planned behavior (TPB), which has been widely used to explain and predict people's behavior or intention to perform a behavior, is used as the theoretical framework for the study. Referring to the TPB framework, this study summarized factors into individual factors, perceived social factors and perceived contextual factors. Furthermore, the authors suggest extending the TPB framework by including teachers' understanding of the reform ideas to facilitate its application in order to explore factors in reform contexts. Lastly, this study discusses several important factors that help teachers to implement new teaching methodologies continually, thus promoting the sustainable implementation of reforms.Sustainability 2020, 12, 1 2 of 21 trend towards over emphasizing knowledge delivery and putting more emphasis on students' active participation to develop their abilities such as collecting and processing new information, gaining new knowledge independently, analyzing and solving problems, and communicating and cooperating with others" [10]. The newest version of the curriculum standard was published in 2011 [11], and the goal of mathematics education was extended from two basics (basic knowledge and skills) to four basics (basic knowledge, skills, mathematical thinking and activity experiences). The standard suggests various instructional approaches to improve students' learning, e.g., self-learning, collaborative learning and inquiry-based learning [11,12]. However, despite the appealing proposals in curriculum reform, research finds that little change is happening in classrooms [13,14]. He and Gao [15], for instance, analyzed 15 middle school mathematics lessons and pointed out that although teachers accepted the reformed model of learner-centered instruction, lecturing still occupied most of their class time. Li [16] found teacher-fronted instruction to be the dominant practice in classes under educational reform, with little interaction between teachers and students. Many Chinese educators call this situation "walk [ing] the old road with new shoes" [12,17].In recent years, while the implementation of national curriculum reform has moved from centralization to decentralization, with decreased control by the central government and more encouragement for developing local curricula by local educational authorities and communities, successful reform cases have been reported at the local level. The D...