Over the past two decades, Turkey has initiated a reform movement to change her classroom assessment system to accommodate performance-based alternative assessment methods in schools. However, research investigating the impact of assessment reform on learning and teaching in schools report that performance assessment approaches have not been implemented effectively. This study investigated the teacher related factors behind the adoption decisions of teachers of these changes introduced. Data for the study were collected through interviews with 53 biology teachers in 24 schools. According to the findings, teachers' lack of self-agency, superficial understanding of the ideas introduced, mistrust that the innovations will work in practice, skepticism about the need for a change and inadequate knowledge and abilities as a result of ineffective dissemination and professional guidance were the main factors affecting the success of the reform. Suggestions to overcome barriers to reform and implications of the findings in managing change are presented and discussed at the end of the paper.