Measuring kindergarten readiness is essential to identifying children who would benefit from additional supports, either in kindergarten or in the years before kindergarten entry. Several measures of kindergarten readiness are in use now by states and researchers. Most assess individual children at the time they enter kindergarten, using teachers and/or child development specialists as assessors. In contrast, a new measure, still in the pilot phase, measures children in the aggregate in the years before they enter kindergarten (ages 3, 4, and 5), using parent responses to the National Survey of Children's Health. This brief is one in a series exploring the pilot measure, known as the Healthy and Ready to Learn (HRTL) National Outcome Measure (NOM). National Outcome Measures (NOMs) cross all population domains and reflect maternal and child population health status. This particular brief reviews the current status of and evidence for the HRTL measure developed as a proposed National Outcome Measure (NOM) for the federal Title V Maternal and Child Health Services Block Grant, and compares it with other well-being and readiness measures. Its purpose is to aid researchers, policymakers, and early childhood advocates in understanding the utility of the new HRTL measure, by itself and in conjunction with other measures of kindergarten readiness. The brief also aims to facilitate appropriate interpretation of future findings from the HRTL measure and recommends next steps in the development of the measure.