INTRODUCTION
Early childhood development is a driving force for sustainable development due to its multiplier effects not only on children but also on the community and society at large (Britto, Yoshikawa and Boller, 2011). Sustainable Development Goal (SDG) Target 4.2 emphasizes the importance of access to high-quality early childhood education and care (ECEC) as a means of achieving equity and transforming lives through education. At the heart of this ambition is a key message: access to ECEC alone is insufficient for achieving positive child outcomes - it must also be of high quality. As a result, meeting target 4.2 means developing methods to accurately measure and monitor quality standards in ECEC. This Brief aims to summarize the key points of ongoing debate on this issue, and outline some of the challenges faced by high-income countries.