This research is part of the summative evaluation of the CPB-PBS Ready To Learn Initiative, which is supported by the U.S. Department of Education. The goal of the Ready To Learn Initiative is to develop engaging, high-quality educational programming and supports for two- to eight-year-old children living in low-income households. During the 2010-2015 grant cycle, Ready To Learn aimed to deliver early mathematics resources on both established technologies (computers, video displays, and gaming consoles) and emerging digital platforms (tablet computers, interactive whiteboards, and smartphones) to create anytime-anywhere learning experiences that leverage the unique capabilities of transmedia for young children's learning. For the purpose of this study, transmedia means the use of familiar characters, settings, and narrative themes or stories across different media formats, such as digital video and interactive online games. As the summative evaluation team for CPB-PBS Ready To Learn, Education Development Center (EDC) and SRI Education (SRI) document and, whenever possible, measure the impact of PBS KIDS transmedia mathematics resources on children's school readiness. (author abstract)