This study investigated issues surrounding the implementation of competence based curriculum in Tanzanian secondary schools. The specific objectives of the study were to examine the teachers' understanding of the objectives of competence based curriculum; to investigate the teachers' abilities in preparing competence based lesson plans; to examine whether or not teachers involved students in classroom activities; and to find out whether or not teachers practiced formative students' assessments as per the requirements of competence based curriculum. The respondents included 186 teachers who were randomly selected from 13 secondary schools found in Mbeya region of Tanzania. The data were collected through interview schedules, observation schedules, and review of documents. The collected data were analysed using thematic content analysis. The findings indicated that the majority (86%) of the interviewed teachers did not have the proper understanding of the objectives of competence based curriculum. In addition, the majority (78%) of the reviewed lesson plans did not reflect the qualities of a competence based lesson plan. Moreover, the involvement of students in classroom activities by the teachers who were observed was, in overall, very low. Lastly, teachers practiced formative students' assessments in less than 50% of the observed classroom sessions. In view of these findings, it seemed that the implementation of competence based curriculum in the selected schools was ineffective. In view of these findings, it is recommended that regular training for in-service teachers should be conducted in order to enable them acquire up-to-date teaching skills as required by the changes introduced in the school curricula.