Despite the growing interest in supporting learning through play across many low and middle-income countries, measures of how contexts can support learning through play are lacking. As part of the Playful Learning Across the Years (PLAY) project, the concept of “self-sustaining engagement” was identified as central to learning through play. That is, learning through play is effective because children are deeply engaged in their learning and are self-motivated to learn. The PLAY toolkit was designed to measure how settings – particularly adult-child interactions in those settings – support children’s self-sustaining engagement in learning. The toolkit was developed for use in multiple age-groups across different settings. For the 0-2 age-group, the toolkit assessed support for children’s engagement in the home, largely through interactions between the caregiver and child. These interactions were assessed through observations and through an interview with the caregiver. In the 3-5 age-group, tools were developed to measure support for engagement in the home and the classroom. Tools for the 6-12 age-group were focused only on the classroom. The classroom-based tools had several components. Teacher-child interactions were assessed through observations, a teacher survey and – for the 6-12 age-group only – a student survey. There was also a classroom inventory to assess physical aspects of the classroom – such as materials on the walls – which might support self-sustaining engagement in learning. The toolkit was developed in three phases – the Build phase used qualitative data to understand local concepts of self-sustaining engagement. The Adapt phase used cognitive interviewing and small-scale (approx. 25 schools, centers or homes) quantitative data to refine the tools. In the Test Phase we used large-scale (approx. 150 schools, centres or homes) quantitative data to assess the psychometric properties of the tool. This presentation focuses on these psychometric analyses. Data were collected for the 6-12 age group from Kenya, Ghana and Colombia; for the 3-5 age group from Colombia, Jordan and Ghana; and from Colombia only for the 0-2 age group. Results indicate how the concept of “support for self-sustaining engagement” can be divided into constituent sub-scales and how the different methods of assessment – observation, teacher report and student report – relate to one another. We will discuss plans to develop a final toolkit, based on these analyses, which can help strengthen the evidence base on learning through play.