This mixed-methods study examined the lived experience of adult English Language Learners (ELLs) in classrooms led by native speaking teachers, compared with their experience in classrooms led by non-native teachers. The socio-cognitive approach to language and emergent common ground framed the development of the English classroom as a Community of Practice, in which students produced varying levels of complex, formulaic, metaphorically dense speech. Both written and oral language production, in conjunction with teacher practices and student behaviors and opinions, served as evidence of differences between the two types of teacher, as well as providing measures of teacher effectiveness. The findings suggested: 1) Native speaking and non-native speaking teachers have different advantages in the classroom, 2) Student success is more closely related to teacher practices than to inherent features such as teachers' native status, and 3) Students felt a connection to their non-native teachers as fellow ELLs, and expressed this relationship through the use of pronouns to position themselves as members of a common community. These findings have led to the conclusion that there is no empirical evidence to support the practice of preferring native-speaking English teachers to their non-native counterparts. Based on the findings, several recommendations for effective teacher practice and implications for further research are suggested, particularly regarding: 1) Effective methods for including natural language and authentic materials in the classroom, 2) The value of play in language learning, and 3) The connections between metaphorical speech and speakers' language and culture of origin. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]