教师效能感是影响教学活动和学生学习成果的重要因素。教师效能感高的老师对学生的学习成绩有积极影响。因此在教师教育领域，学生教师在教师教育期间，尤其是教育实习期间,教师效能感的发展变化受到了很大的关注。然而，前人的研究并未得到一致的结果。有的研究表明教育实习阶段学生教师的教师效能感有所提高，但有的研究表明学生教师的教师效能感在教育实习阶段有所下降。关于教育实习期间学生教师的教师效能感变化还需要进一步研究。此外，前人的研究大多是量化研究，质性的个案研究很少。 本文是一篇质性研究，主要研究了三位职前英语教师在顶岗实习期间教师效能感的变化以及产生这些变化的原因，旨在为更好的实施教育实习，提高学生教师的教师效能感提出建议。本文所使用的教师效能感框架包含三个要素：指令技能，课堂管理，和学生参与度。研究对象是来自中国北方一所师范大学的三名大三学生，研究工具主要包括访谈，教学反思日志，以及关于课堂实录的刺激性回顾。数据分析方法为主题分析法。 在每个教师效能感要素之下，本研究总结出十个二级要素，进一步完善了教师效能感框架。研究结果表明顶岗实习对职前英语教师教师效能感的影响并非总是积极的，顶岗实习之后，职前英语教师某些方面的效能感有所下降或者持续偏低,如学生教师在帮助学生提高英语成绩方面的效能感有所下降。产生这些变化的原因主要分为内因和外因，其中导师因素，实习学校的环境以及学生因素对职前英语教师的教师效能感产生的影响最大。 最后，本研究对如何提升教育实习效果，提高学生英语教师的教师效能感提供了一些启示。对于学生教师而言，他们要在顶岗实习之前打好坚实的理论基础，并注意提升自己的英语语言水平，还应该在实习期间多听听有经验的老师上课。对于组织顶岗实习的学校而言，应该为学生教师挑选合适的实习学校和有经验的指导老师。

Teacher efficacy has been found to be an important influencing factor on teacher activities and student outcomes. Teachers with high teacher efficacy tend to have positive influences on students’ performance. Therefore, the development of student teacher’s teacher efficacy during their teacher preparation period, especially during the teaching practicum period, has attracted much attention in the field of teacher education. However, results of previous studies are inconsistent. Some demonstrate an increase in student teachers’ teacher efficacy during student teaching period while others show a decline. Further studies are needed to explore the development of student teachers’ teacher efficacy during the teaching practicum period. Besides, most of the previous studies are quantitative studies. Qualitative case studies are rarely to be found. The present study is a qualitative study that explores the changes of three preservice English teachers’ teacher efficacy during their student teaching practicum, and the factors that contribute to the changes, aiming to provide some suggestions on how to better conduct student teaching practicum to help improve student teachers’ teacher efficacy. Construct of teacher efficacy applied in the present study consists of three factors: efficacy for instructional strategies, efficacy for classroom management, and efficacy for student engagement. Participants are three third-year students from a normal university in north China. Research instruments include interviews, reflective journals, and stimulated recalls of classroom video tapes. Thematic analysis is conducted to analyze the data. Ten sub-factors of teacher efficacy are founded under each factor of teacher efficacy, which complete the construct of teacher efficacy. Results show that the influence of teaching practicum on student teachers’ teacher efficacy is not always positive. Several aspects of teacher efficacy decreased or remained low after the teaching practicum, such as efficacy for helping students do well in English. Internal and external factors are found to influence the changes of teacher efficacy, among which three factors are found to be the most influential factors, namely, mentor effect, school climate, and student factors. In the end, implications are provided on how to improve teaching practicum effectiveness to develop student teachers’ teacher efficacy. As for student teachers, they have to be theoretically prepared before they begin their teaching practicum, and improve their English language proficiency. They are also expected to observe experienced teachers’ class as much as possible. As for the universities who hold the teaching practicum program, they should choose proper practicum schools and experienced supervisors for student teachers.