While the Lao People’s Democratic Republic has made steady progress in expanding access to quality education, many children still leave primary school with difficulties in reading and writing for their age. Despite this, there are ‘positive deviant’ schools that outperform other schools located in similar contexts and with an equivalent level of resources. This policy brief – about practices aligned with formative assessment in Lao schools – is part of a series that presents important insights from both quantitative and qualitative data on behaviors and practices of a variety of education actors in positive deviant schools in Lao PDR. It also explores existing local solutions and broader evidence emerging from all schools on various education-related challenges. Data Must Speak – a global initiative implemented since 2014 – aims to address the evidence gaps to mitigate the learning crisis using existing data. The DMS Positive Deviance research is co-created and co-implemented with Ministries of Education and key partners. DMS research relies on mixed methods and innovative approaches (i.e., positive deviance approach, behavioural sciences, implementation research and scaling science) to generate knowledge and practical lessons about ‘what works’, ‘why’ and ‘how’ to scale grassroots solutions for national policymakers and the broader international community of education stakeholders.