Competence-based education and training (CBE/T) has been implemented in Ethiopia to develop the competences of (future) professionals and to improve their performance. However, empirical evidence that demonstrates the effectiveness of CBE/T is scarce. Positioning the study within the theory of strategic alignment and comprehensive competence-based training, we used the authentic core job task 'On-Site Helping of Farmers during the Planting of Maize', of Development Agents as problem context and conducted an experimental-longitudinal research study including multirater performance assessment. The study compared competence development of the Development Agents who received training that could be characterized as 'High-CBT' (N = 33) and 'Low-CBT' (N = 32). 'High-CBT' means that in these training programmes, principles of competence-based training were used more completely than in the 'Low-CBT' programmes. Experts rated the competence levels of the Development Agents and Development Agents rated their own competence levels. Both groups did that before and after the training. Individual Development Agent performance was also rated by Trained Assessors. Longitudinally, Development Agent performance data was collected during one production year at three points in time. Development Agent's competence development in the 'High-CBT' training condition was higher than in the 'Low-CBT' condition. Observations made on each Development Agent's performance by Trained Assessors both in the Farmer Training Centres and in the authentic job situations, generally confirmed better performance of the 'High-CBT' group compared with the 'Low-CBT' group. The finding contributes to the state of research on the relationship between competence development and performance improvement, which is theoretically postulated although less empirically tested.