Education and business leaders and the public at large have grown increasingly concerned about the achievement gap between children from at-risk backgrounds and their more advantaged peers – a gap that is apparent even among young children. To date, much of the research and policy attention on achievement disparities has focused on the preschool years (ages 3-5) leading immediately into the transition to kindergarten, or in later elementary school and high school. Research that has explored disparities based on sociodemographic risk factors at earlier ages has indicated that disparities in cognitive development are evident at 24 months of age, with a few studies documenting developmental disparities based on sociodemographic risk within the first year of life. Very little research, however, has used nationally representative data to explore whether disparities are found within the first year of life, and whether disparities are evident across a wider range of developmental outcomes. The data and analyses presented in this brief, however, indicate that disparities are apparent in infancy, with the gap widening in toddlerhood. Policy makers and early childhood professionals therefore need to take into account the entire period from birth to 5 years, including targeted interventions to address the developmental needs of at-risk children ages 0 to 3.