Preschool education is now firmly linked to two aspirational purposes: as the first step on a trajectory of academic and life success for all children and as wise economic policy for the nation. Both purposes are grounded in an assumption that the early developmental boost children receive from preschool will produce lasting impacts. However, efforts to identify enduring impacts of contemporary preschool programs have produced mixed evidence, leading the field to acknowledge that we have yet to adequately understand the essential conditions and processes in early education classrooms that increase the odds that children will flourish in school and thrive in their adult lives.