The purpose of this study is to analyze critically the two main categories of teachers' unions as progressive and aggressive teachers' unions and their positive and negative effects on students' achievements at secondary school level. The researcher therefore determined to find out the exact role of teachers' unions. All secondary school teachers of district Shangla were selected as population of the study while 100 teachers at SSC level from twenty high schools were chosen as sample of the study. For this purpose, simple random sampling technique was used. The main tool for the collection of data was a survey questionnaire. The findings based on the statistical calculations showed that there are two main categories of teachers' unions. Progressive unions play positive role for the progress of education system while aggressive unions play negative and destructive role in education system. Progressive teachers' unions work for the professional development of teachers, support teaching learning process and improve quality of education. On the other hand aggressive teachers' unions work for the increase of salary, promotion, better working condition and defend their unproductive members. All Teachers' unions may consider themselves as an integral part of the education system. They may perform their assigned duties and responsibilities honestly and sincerely.