In view of the increasing number of cases of plagiarism and the ease of use of online published texts, universities are faced with a considerable challenge to prevent and take action against plagiarism in academic student papers. In reaction to plagiarism, web-based plagiarism detection systems (PDSs) are increasingly used to check submitted papers - this checking entails various problems, for example the percentage of plagiarism found is only an indication of the actual extent of plagiarism and not all types of plagiarism can be identified. To cope with this problematic situation the voluntary plagiarism check (VPC), an alternative preventive university didactic concept, was developed at the University of Education, Freiburg (Germany). It focused on the development of individual skills. Students were able to submit their academic papers (e.g. an undergraduate paper, final thesis) anonymously. These were then tested with the PDS Ephorus. Following interpretation and summary of the findings by the project team - plagiarism as well as referencing mistakes - we advised the students on a suitable approach to academic writing based on their own typical mistakes. The VPC was conducted as a three-semester research project and was later evaluated. About 500 academic papers were tested. In 90% of the undergraduates' work incorrect and/or missing citations were found. This high percentage decreased among students in later semesters. Instances of plagiarism were detected in about 40% of the papers when the texts of advanced students (≥6th semester) were tested. At the same time the length of the plagiarised texts decreased. Around half of the students stated that it was acceptable to copy single sentences or short passages from other sources without citation; they did not consider plagiarising on a limited scale as cheating. A similar number of students admitted to having doubts about whether they could write a good paper without plagiarising. Almost all students said that they had experienced considerable uncertainty, stress and fear while writing academic papers. The project results offer new insights into Internet-focused working strategies, on student justification for plagiarism and attitudes to literary property and on frequent mistakes. In addition to showing that there is broad acceptance among students of the VPC, the results can be taken into consideration in curriculum development and in developing courses to meet the needs of students.