This study examined the challenges hindering teachers’ effective implementation of the Competence-Based Curriculum (CBC) in public secondary schools in Meatu District, Simiyu Region, Tanzania. Guided by the Job Demands-Resources (JD-R) Model, the study adopted a qualitative case study design as part of a broader mixed-methods study. The study purposively selected ten public secondary schools, involving 20 participants: 10 Heads of Schools and 10 Academic Masters/Mistresses. Data were collected through semi-structured interviews and analysed thematically through transcription, coding, categorisation, and theme development. The findings revealed four major challenges: inadequate time for lesson preparation and planning, difficulties in conducting continuous assessment and providing timely feedback, limited use of learner-centred teaching methods, and teacher fatigue, stress, and emotional exhaustion. These challenges were associated with heavy teaching loads, large class sizes, extensive assessment and marking responsibilities, administrative and co-curricular duties, and insufficient staffing and instructional support. The findings further indicated that teachers generally recognised the importance of CBC but faced contextual constraints that limited their ability to consistently apply learner-centred and competency-based practices. The study concludes that effective CBC implementation requires supportive working conditions that balance teachers’ job demands with adequate resources. It recommends improving teacher staffing, equitable workload distribution, adequate preparation time, professional development, efficient assessment practices, and school-level monitoring of teachers’ workload and wellbeing.