Previous research has looked into educational approaches to prevent plagiarism in academic writing, yielding insights into how plagiarism can be avoided. However, plagiarism remains a major problem in the education sector. We designed a training module that includes a customised Online Scaffolding Writing System (OSWS) to help faculty teach undergraduates how to avoid committing plagiarism in their academic writing. A quasi-experimental design was used to analyse the plagiarism-related perceptions and behavioural changes of 121 undergraduate students and to test the effects of the new module on students' academic writing. The experimental group performed significantly better than the control group in terms of decreasing the extent of plagiarism in their writing (with a mean decrease from a moderate to minor level of plagiarism), and improving their writing quality (with a mean increase of 18 percentage points in writing scores). Furthermore, more than 95% of the students in the experimental group and their instructor reported that they valued the benefits of adopting the training module in class, and almost 90% of them expressed high levels of satisfaction with the learning they had obtained from the OSWS. This study also provides insights into how the new training module can be implemented across disciplines.