Management by Objective through Open Performance Review and Appraisal System (OPRAS) was introduced in Tanzania for evaluation of public servants work performance in 2004. The aim of this study was to investigate how teachers perceive the implementation of OPRAS as a mechanism of assessing their work performance and making them accountable for their teaching. The study was mainly qualitative with some aspects of quantitative data. It involved 108 informants, where 90 were the primary school classroom teachers, 10 headteachers, 6 school committee members and 2 district educational officials. The data were collected through questionnaires, interviews, and focus group discussion. Some teachers think if OPRAS contract could well be worked out, it could improve the performance; however, there are those teachers who think OPRAS is impractical and unrealistic to the Tanzanian context where pupils are congested in classrooms with shortage of desks. During the school visit in both Kinondoni Dar es Salaam and Mbeya City findings indicated that OPRAS had been abandoned as it created hostility between headteachers and teachers. Teachers complained of the expenses involved in duplicating the copies and the time consumed for discussion. I argue in this paper that although evaluation of teachers is important, the adoption of the type of assessment for their work performance has to be considered because of the nature of the field and the complications involved in dealing with the human mind. Teaching is a labour-intensive process. Teachers cannot, by means of their teaching, determine how many pupils will pass a given exam and how well they will do in their exams under the OPRAS requirements.