This paper observes on-the-job training as a determinant gadget for teachers’ productivity in Lagos, Nigeria. It explained the concept of human resources development and its importance to organizational goal attainment and development. It also highlighted the concept and types of training, the need for staff training and development in the education sector, management training and teachers’ development agencies in Nigeria. It further analyzed the concept of productivity. It gave an insight on the impact of on-the-job training as a determinant gadget for teachers’ productivity. Recommendations were given. It was concluded that apart from all other motivating factors, the most determinant gadget for the enhancement of teachers and other staffs’ productivity is on-the-job training. And that through on-the-job training, teachers and any staffs can acquire positive and necessary skills and additional knowledge that in turn enhances and improves his/her job responsibilities.