The purpose of this study was to explore some problems and desires of developing self-confidence in teaching English of non-English major teachers in rural small primary schools in Thailand with participatory action research. This study also aims to develop teacher's confidence in teaching English, enhance communicative competence and to assess effectiveness of teaching English of non-English major teachers in the rural small primary schools in Thailand with participatory action research. 5-step procedure of the research included; pre-research phase, planning phase, research phase, verification and reflection phase and monitoring and evaluation phase. There were 6 methods for developing teachers this include; direct training, self-direct learning, teacher networks, coaching and mentoring, informal meeting and, and school visit. The results revealed that the operation through a semester lead the development of the 6 approaches to elevate non-English major teachers' confidence in teaching English, and also enhance their communicative competence in order to makes teaching more effective. The results were: Non-English major teachers had self confidence in teaching at high level (X-bar = 4.41) ; Non-English major teachers had communicative competence at a higher level (X-bar = 3.54) , the pre-test score was 28.33% and the post-test score was 67.08%; in order to assess the effectiveness of teaching, non-English major teachers who graduated from major field finished their tasks with observations, both participatory and non-participatory research throughout the one year assessment of students' achievement. The students' achievement showed higher effectiveness including 2013 and 2014 English achievement. It showed that students at Ban Khok Klang School gained higher achievement approximately 3.47% with 4.41 standard deviation. Those students at Ban Lao-ngong School gained 3.72% higher than pre-test average with 1.60 standard deviation. It showed that the effectiveness of teaching was higher. All 6 approaches could be supported to elevate self-confidence for non-English major teachers in small primary schools in teaching and communicative competence, and also to improve effective teaching.