The National Institute on Out-of-School Time (NIOST) at the Wellesley Centers for Women received funding from the William T. Grant Foundation to test and strengthen the Assessment of Afterschool Program Practices Tool (APT). The APT was designed to measure key aspects of afterschool program quality believed to contribute to desired youth outcomes. Based on extensive field testing conducted by NIOST in 2005 in Massachusetts 21st Century Community Learning Center programs, the research version of the APT was converted into a self-assessment tool and has received favorable feedback from practitioners in the field. This study will test the APT’s stability and accuracy as a measure of afterschool program quality, including the extent to which observer characteristics (such as whether the observer is a practitioner from the program), affects ratings of quality. The study will also examine how observer ratings of quality compare with youth reports of their program experiences, and will explore the relationship between ratings of quality and a limited number of youth outcomes. APT testing will occur in 25 afterschool programs serving grades K–8 in the Greater Boston area. It is hoped that the results from this study will enable practitioners to more accurately and reliably measure and track progress with program improvement efforts and more effectively target and promote youth outcomes.