This study investigates teacher attitudes about language and education. The purpose of the study is to help program designers develop professional development efforts that successfully address some of the major identified challenges teachers face when transitioning into Mother Tongue Based Multi-Lingual Education (MTBMLE), including negative attitudes. It also suggests protocols and issues that trainers should consider when designing professional development for MTBMLE teachers. The research question guiding this study is: (1) Do teachers' attitudes towards and knowledge about mother tongue-based instruction change after they participate in professional development that is consistent with good professional development practice? (a) What were teachers' knowledge and attitudes about MTBMLE before the professional development program? (b) Did teachers' knowledge and attitudes change after participating in the professional development program? (c) Why did teachers hold particular attitudes towards MTBMLE prior to professional development and what factors influenced their change? I conducted this research during a three-month MTBMLE professional development program with a group of indigenous first grade teachers and their school principals in Save the Children's outreach areas in rural Mindanao in the Philippines. I used a "Q" sort methodology for initial interviews conducted with a subset of five first grade teachers followed by a second interview after the professional development program. The interview data showed that teachers came into the trainings with two distinct viewpoints; mother tongue supporters and one mother tongue resister. After the professional development program, however, teachers were all more positive about using the mother tongue as the language of instruction. Interviews revealed that teachers were more positive and confident in teaching the mother tongue when they had the opportunity to: (1) spend time learning about their own language, (2) create mother tongue teaching and learning materials, and (3) reflect on their early learning experiences and experience what it is like to learn in a language that is not familiar. This paper will discuss the research findings in depth and will provide a clearer picture of how to train and support teachers who are transitioning into MTBMLE. [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.]