This study investigated the effects of Native English-Speaking Teachers (NEST) and Non-Native EnglishSpeaking Teachers ( NNEST) on students’ English proficiency and perceptions. The research methodology employed an observational study based using critical applied linguistic. Data collection was through a mixed method. The tools used were the Cambridge English: Key English Test (KET), classroom observation evaluation forms, and interviews. The participants consisted of 252 upper primary students from one private school in Chiang Mai, Thailand, during the academic year 2019. Results indicated that students’ English proficiency was increased significantly at .01 level in both groups. The gain score suggested that NNEST can make a higher gain score than NEST in all grade levels. Student’ s answers show NNEST score a higher agreeability towards teachers’ teaching abilities, English abilities, and the creation of an engaging learning atmosphere over NEST. Classroom observations implemented by three English Learning Teachers confirmed the results that NNEST is more agreeable than NEST in teachers’ teaching ability and motivating learning atmospheres in classrooms. However, in teachers’ English skills, the experts’ perceptions were opposite that of the students. Lastly, the interviews with the students reflected three key aspects: their preferences of English teacher advantages, disadvantages, and strengths of both NNEST and NEST.

中文翻译：

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母语为英语的教师和非母语为英语的教师对学生英语水平和感知的影响的观察性研究

本研究调查了母语为英语的教师 (NEST) 和非母语为英语的教师 (NNEST) 对学生英语熟练程度和认知的影响。研究方法采用基于使用批判性应用语言的观察性研究。数据收集采用混合方法。使用的工具是剑桥英语：关键英语测试 (KET)、课堂观察评估表和面试。参与者包括 2019 学年泰国清迈一所私立学校的 252 名高小学生。 结果表明，两组学生的英语水平显着提高了 0.01 级。增益分数表明 NNEST 在所有年级都可以取得比 NEST 更高的增益分数。学生的回答表明 NNEST 对教师的教学能力、英语能力以及在 NEST 上营造一种引人入胜的学习氛围的认可度更高。三位英语学习教师进行的课堂观察证实，NNEST 在教师的教学能力和课堂学习氛围方面比 NEST 更受欢迎。然而，在教师的英语技能方面，专家的看法与学生相反。最后，与学生的访谈反映了三个关键方面：他们对 NNEST 和 NEST 英语教师优势、劣势和优势的偏好。三名英语学习教师进行的课堂观察证实了NNEST在教师教学能力和课堂学习氛围方面比NEST更令人愉快的结果。然而，在教师的英语技能方面，专家的看法与学生相反。最后，与学生的访谈反映了三个关键方面：他们对 NNEST 和 NEST 英语教师优势、劣势和优势的偏好。三位英语学习教师进行的课堂观察证实，NNEST 在教师的教学能力和课堂学习氛围方面比 NEST 更受欢迎。然而，在教师的英语技能方面，专家的看法与学生相反。最后，与学生的访谈反映了三个关键方面：他们对 NNEST 和 NEST 英语教师优势、劣势和优势的偏好。