Children's school readiness as they enter kindergarten is an important predictor of their academic success and ultimately their long-term health and economic outcomes. Research shows that participation in high-quality early childhood education helps preschoolers gain the foundational language and literacy skills as well as the social-emotional competencies they need to be ready for kindergarten. Even so, free or affordable high-quality preschool options remain limited for families in many underserved communities. Jumpstart is a nonprofit organization that aims to address the school readiness gap. It partners with early childhood education centers across the country to increase their capacity to provide high-quality language and literacy instruction to children in underserved communities. This report presents the findings from an evaluation of Jumpstart's Foster Grandparent Program (JFG) in Los Angeles and Compton, California, which operated from fall 2011 to summer 2019, where Jumpstart's services were delivered by older adults. The evaluation, which focuses on the 2017-2018 academic year, examines whether the JFG program was implemented as intended and to what extent the presence of volunteers enhanced children's educational and developmental experience in the classroom. This evaluation found that: (1) The Foster Grandparents had consistently high attendance at training sessions and reported feeling adequately prepared to provide services to children; (2) The Foster Grandparents demonstrated a strong commitment to the program, and children experienced an increased number of adults in the classroom; (3) The Foster Grandparents implemented the curriculum-based sessions regularly and as intended; (4) The Foster Grandparents devoted a high number of hours to child-centered time (CCT); and (5) Children who received services from volunteers made gains in language and literacy development. [This report was written with Alec Gilfillan and Sara Staszak.]