The William Penn Foundation launched Philadelphia's Informal Learning Initiative (ILI) to support the development of literacy-rich programming for families with children aged 3 to 9. The initiative was designed as a network of partnerships in which a cultural organization--usually a museum--paired with one or more, community-based organizations (CBOs) to design literacy-rich informal learning experiences for caregivers and children. The initiative involved 11 cultural partners and 15 CBOs. Programs exposed three- to nine-year-old children and their families to literacy practices in the context of original artwork, live animals, science experiments, natural settings, new foods, and cultural or historical sites. Programming was delivered at no cost to families, often in community settings such as recreation centers or school auditoriums. Convenient times and locations, as well as snack or meal options, supported family participation, as did book giveaways, take-home activity packs, and special museum visits. As the evaluation team for ILI, the authors structured their work to support the development of a networked community of practice, collecting data for improvement and exploring the best ways to measure impact across projects. They used a structured observation protocol and CBO staff- and educator-conducted interviews with children and caregivers in their programs to determine ILI programming's impactfulness. The study aimed to examine how museums can connect to collective impact efforts in literacy and how informal learning programs can be reoriented to better respond to community needs. Findings from the study and recommendations for museum-CBO partnerships are discussed.