Background: This article reports on a mentoring programme which was implemented in selected Scottish secondary schools with the view to supporting students with school work, transition to further education/higher education, careers, and interpersonal skills. Mentoring students can enhance their academic, social, career and other outcomes. Mentoring relationships, when properly implemented, have been found also to yield positive results for mentors. Purpose: This paper is an investigation into a school-based mentoring programme which was implemented in 6 selected Scottish secondary schools. In so doing, we hope to contribute to an evolving framework for designing and implementing successful school-based mentoring. Sample: The sample for this study included 10 students aged between 16 and 17 years old in the second year of a broader 2-year business/education project, which aimed to promote student uptake of science, technology, engineering and mathematics (STEM) careers after secondary school. There were 11 mentors, who were drawn mainly from the science, health and the education sectors. Design and method: Methodologically, this study was qualitative interpretivist in nature. Data collection involved focus group discussion and individual semi-structured interviews. Results: The findings show mentee and mentor preparation, clarity of expectations, mentee-mentor matching, mentee motivation, appropriateness of meeting spaces and power relations, modes of communication including the use of social media, and the role of schools as essential conditions which influenced the quality of mentoring relationships. Conclusion: The findings suggest that mentoring programmes involving students in school and "external" adult mentors need to consider a range of factors to achieve success when designing and implementing mentoring. This paper raises important issues for example, communication using social media, which have implications for practice in business sector and school partnerships involved in school-based mentoring.