In 1994, Uganda's Ministry of Education and Sports introduced Teacher Development Management Systems, with the sole aim of supporting and enhancing professional development of teachers through in-service teacher training. Though the training has increasingly motivated teachers into upgrading their academic qualifications, research has not established the effect of the training on professional development of teachers and loopholes, assumptions and misconceptions still persist two decades after the inception of the Teacher Management Systems. Using primary data collected in 2016 from the southwestern Uganda districts of Bushenyi, Rukungiri and Sheema, this study attempts to examine this issue. Key informant interviews and questionnaires were used to collect data from a sample of 610 primary teachers and education stakeholders selected for the study. Findings show that in-service teacher training has a significant effect on teachers, particularly on their academic qualifications, performance, and professionalism. However, these benefits can only be realized when the training is properly planned, implemented and continually evaluated, and in the presence of certain resources and incentives. To this end, the study recommends a review of teacher training approaches and a revamp of school environments to facilitate the teaching-learning process.