Much well-deserved attention in K-12 Computer Science (CS) education has focused recently on the successful launch of the College Board's new AP CS Principles course, which is breaking participation records and broadening CS participation. To further leverage the national investment in a successful high school CS program, however, it is important to create, sustain and study a continuous CS pipeline that begins early and spans all grade levels. This experience report articulates the characteristics of Code.org's K-5 CS Fundamentals (CSF) program and summarizes the experiences of adopting the CSF curriculum to support large-scale, university-driven K-5 Professional Development (PD) programs across two states in different geographical regions of the USA. An overview of Code.org's CSF curriculum and PD survey data is provided, followed by a summary of each state's experience. A set of lessons learned offers recommendations for those considering implementation of statewide PD programs in K-5 CS; future plans are discussed to investigate observations from this experience report within a formal research setting.