The paper addresses the challenges of evaluating the impact of business coaching programmes with a varied portfolio of firms working across sectors and countries. Observable indicators of changes in business management practices are rarely relevant across sectors. Therefore, evaluators need to rely on the perceptions of the managers who have received coaching. We designed an online survey to compare the effectiveness of business coaching within a portfolio and across programmes. The survey was applied to the portfolio of two private sector development programmes. We derived so-called ‘contribution scores’ from individuals’ perceptions of how business management practices had changed and their perceptions of the role of business coaching in bringing about these changes. The survey included some features to reflect on response reliability. We show that the tool seems fairly reliable for comparative analysis and helped to identify the types of firms and contexts where business coaching support appears more effective.