BackgroundDelivery of quality reproductive health services has been documented to depend on the availability of healthcare workers who are adequately supported with appropriate training. However, unmet training needs among healthcare workers in reproductive, maternal, and newborn health (RMNH) in low-income countries remain disproportionately high. This study investigated the effectiveness of trainings with onsite clinical mentorship towards perceived importance and performance in RMNH among healthcare workers in Mwanza Region of Tanzania.MethodsThe study used a quasi-experimental design using single group pre-and post-intervention evaluation strategy. The training needs of healthcare workers from the selected health facilities were assessed, skills gaps identified and ranked according to priority. Training courses that addressed skills gaps were developed and delivered with adaptations of the national guidelines followed by onsite clinical mentorship for one year. The baseline and endline survey were conducted at 3 years interval to assess change in HCWs on their perceived importance and performance on different aspects of RMNH care. Independent samples t-tests were used to compare differences in perceived performance in selected training areas between baseline and endline. Significance was set at p < 0.05.ResultsTNA was administered to 152 and 216 healthcare workers at baseline and endline respectively. In total, 141 (65%) of the 216 end line survey participants had received at least one IMPACT project training course and at least three mentorship visits. Participants were matched on their age and duration in RMNH services, but differed in age and duration of employment. Comparison between baseline and endline by using the training needs analysis questionnaire scores showed statistically significant positive changes (p ≤ .05) in most training needs analysis items, except for some items including those related to research capacity and provision of health education for cancer.ConclusionsThe findings revealed that the training and onsite clinical mentorship program that address the actual needs of healthcare workers to have significant positive changes in perceived performance in a wide range of RMNH services. However, further studies with rigorous designs are warranted to evaluate the long-term effect of such training programs on RMNH outcomes.