This paper describes the research protocol for the Educational and Developmental Gains in Early Childhood (EDGE) Study, which will examine the implementation of two years of funded kindergarten prior to the first year of school in Victoria, Australia. EDGE will examine whether children's language, cognitive, social-emotional, and behavioural outcomes are improved after two years of kindergarten compared to one year. The experiences of (and impacts on) teachers, service leaders, and families will also be examined. The study includes a cross-sectional cohort of 95 early childhood education and care (ECEC) services, and an embedded longitudinal observational cohort of children attending these services. Case studies of 15-20 ECEC services will also be collected, in addition to interviews with policy stakeholders.