Background
Train-the-trainer (TTT) programs are widely applied to disseminate knowledge within healthcare systems, but evidence of the effectiveness of this educational model remains unclear. We systematically reviewed studies evaluating the impact of train-the-trainer models on the learning outcomes of nurses.

Methods
The reporting of our systematic review followed PRISMA 2020 checklist. Records identified from MEDLINE, Embase, CINAHL, and ERIC were independently screened by two researchers and deemed eligible if studies evaluated learning outcomes of a train-the-trainer intervention for trainers or trainees targeting nurses. Study quality was assessed with Joanna Briggs Institute’s critical appraisal tools and data of study characteristics extracted (objective, design, population, outcomes, results). Heterogeneity of outcomes ruled out meta-analysis; a narrative synthesis and vote counting based on direction of effects (p < 0.05) synthesized the results.

All records were uploaded and organized in EPPI-Reviewer.

Results
Of the 3800 identified records 11 studies were included. The included studies were published between 1998 and 2021 and mostly performed in the US or Northern Europe. Nine studies had quasi-experimental designs and two were randomized controlled trials. All evaluated effects on nurses of which two also included nurses’ assistants. The direction of effects of the 13 outcomes (knowledge, n = 10; skills, n = 2; practice, n = 1) measured in the 11 included studies were all beneficial. The statistical analysis of the vote counting showed that train-the-trainer programs could significantly (p < 0.05) improve trainees’ knowledge, but the number of outcomes measuring impact on skills or practice was insufficient for synthesis.

Conclusions
Train-the-trainer models can successfully disseminate knowledge to nurses within healthcare systems. Considering the nurse shortages faced by most Western healthcare systems, train-the-trainer models can be a timesaving and sustainable way of delivering education. However, new comparative studies that evaluate practice outcomes are needed to conclude whether TTT programs are more effective, affordable and timesaving alternatives to other training programs.