我們以診斷教學實作做為學習教學的目標，在學校的教學實作社群內，探討一位實習教師的學習動機、身份地位、反思和教學知能的成長之間的關聯，進而建構個案教師學習教學的模型。研究採個案研究法，主要採質的詮釋。在信度與效度方面，我們使用觀察實習教師的教學、訪談實習教師、訪談學校輔導教師、以及分析實習教師的反思報告和學生的回饋資料來進行三角校正。研究發現，這位實習教師有強烈的內發學習動機，但是實習剛開始時，由於他缺少診斷教學實作經驗，教學知能尚不足，想要引起師生互動的教學容易受到挫折，容易受到輔導老師和學生對他的教學感受的影響，導致無法有效提升他的教學知能。實習教師從教學行動中所察覺到的教學問題，引動他的內發學習動機，讓他自主地去觀摩多位老師的教學，和研究者討論教學問題，吸取他人的教學相關經驗。同時，他在寒假期間也主動爭取到救國團和國中為國中生上課的機會，第二學期主動主持班級討論會和讀書會，累積他實行診斷教學策略的相關教學知識。最後終於在課外教學活動中，經驗了診斷教學實作。研究者從研究結果建構個案教師學習教學的模型，發現教師在實作社群中的自主與他律的身份會相互擠壓，教師的內發動機和外誘動機則不會互相擠壓，在教學過程中教師的反思層面漸廣。在教師的動機、身份和反思三者的連動下，教師的教學知能日豐。

Setting the probationary school as base of the community of practice, this paper intended to explore the relations of motives, social identities, reflections and pedagogical content knowledge (PCK) of a probationary teacher. This is a case study. Our interpretations are based on the data collected from classroom observing and regularly interviewing this probationary teacher, interviewing his mentor teacher, analyzing his probationary reports, teaching journal and his students’ feed-back questionnaire. We observed that the probationary teacher has very strong motives in learning to teach. However, his intention of teaching diagnostically was defeated by his relatively weak PCK and easily impacted by the traditional instruction approach at the beginning stage of his probation. His social identity within the community of practice is heteronomous. He was not able to practice intentionally at this early stage. Gradually, he suffered in his classroom by the ignorance of his students to his instruction and awared that his teaching must have crucial problems. His strong intrinsic motives lead him to search for learning opportunities within the community. He was able to observed many lively mathematics classrooms which are identified by his survey and asked for permissions. He also created a weekly regular tutoring lesson for his students. His PCK was growing under those actively learning activities. A diagnostic teaching approach has been observed during his tutoring lesson. Based on our data, we reviewed the model of learning to teach of this probationary teacher. Within the context of practice, the autonomous identity and the heteronymous identity of a teacher will be pressing each other, the intrinsic and extrinsic motives of a teacher are compatible, and the quality of a teacher’ reflections is extending. The growth of this teachers’ PCK was resulted by the interactions of his motives of learning, his social identities and the quality improving of his reflections.