In the past decade, evidence-based practice has led to a more critical approach towards professional practice in the humanitarian working field. Many agencies have increased their capacity and resources to research intervention effectiveness and programme impact. When evaluating psychosocial interventions, practitioners and researchers are often not only interested in intervention outcomes, but also in the external factors that influence effectiveness, the intervention process and the views of its beneficiaries. This requires a practice-driven approach that takes into account the (cultural) reality in the field, collects relevant process information and provides a framework to reflect the views of the participants. This paper explains how War Child Holland developed a participatory Monitoring and Evaluation (M&E) tool to evaluate I DEAL, its psychosocial life-skills intervention. The aim of the tool was to research intervention effectiveness by collecting process information with children as the key informants. The participatory M&E tool comprises a range of qualitative and quantitative measures, such as setting personal goals, themed quizzes, module evaluations and impact mapping. The tool was piloted with 510 children and 120 parents in Northern Uganda. It was found that the M&E tool has potential to strengthen ‘evidence-based’ evaluative practice and to involve children in meaningful evaluation, but it was found to be difficult to gather more data for impact evaluation without further quantifying and expanding the tool.