Teachers’ participation in decision making plays significantly in their work performance. In Tanzania, the idea of participation in decision making emerged from decentralization policy and adopted in the field of education through Education and Training Policy of 1995. This study sought to find out the relationship between teachers’ participation in decision-making and their work performance, identified the factors affecting teacher’s participation in decision-making and work performance and propose strategies to enhance teachers’ participation in decision-making. Moreover, the study adopted mixed research approach specifically convergent parallel to collate data from teachers, heads of schools, WEOs and DEO for secondary schools. Validity and reliability of quantitative instruments were tested through content and appearance whereby 0.82 correlation coefficient were obtained to indicate the instruments were valid and reliable. Likewise, reliability of qualitative tools was obtained through triangulation system. Quantitative data were analyzed through computer software program known as SPSS version 20 while qualitative data were analyzed through content analysis methods. The findings demonstrated that there is a relationship between teachers’ participation in decision making as it increases efficiency, commitment, accountability and enhances students’ performance. Moreover, the study indicated that teacher’s participation in decision-making is affected by inadequate time for participation, financial challenges, facilities, transparency and lack of leadership training. These factors led to poor academic performance in schools. Furthermore, the researcher recommended that there should be increase of transparency, provision of adequate facilities, workshops and seminars as well as motivation for teachers to deal with the factors affecting teachers’ participation in decision making to boost their work performance in public secondary schools.