The question of how the U.S. will develop a citizenry with the skills necessary to meet the challenges of the 21st century has attracted the attention of legislators, scientists, and educators. Answering this question leads inevitably to its roots: how well are we preparing young children to enter kindergarten ready to learn? Educators in k-12 school systems are faced with wide disparities in skill levels of entering kindergarteners, which means that all too many children are already far behind many of their peers. Findings in developmental science point toward the importance of early-life experiences in shaping brain development and suggest that if we knew how to provide these experiences in our early education programs, we could have a lifelong impact on children's success. The quality and reliability of early experiences and environments are the building blocks of early brain architecture. Parents and trained adult caregivers who are in tune with a child provide the "serve and return" stimuli through conversation, interactive play, guided exploration, and orderly progression that serve as the raw materials of early child development. Unfortunately, in many neighborhoods, violence, lack of services, and the stresses of poverty combine to make it difficult for a family to provide optimal stimulation and stability during a child's early years. The result is that a disproportionate number of children from low income families lack optimal environments and stimulating experiences and thus enter kindergarten already behind their peers in intellectual and social-emotional development. In recent years, families across the entire income spectrum have experienced increasing stress due to such challenges as making financial ends meet, working multiple jobs, and/or raising a child as a single parent. The good news, according to numerous studies, is that children attending publicly-funded pre-kindergarten programs are better prepared for kindergarten than similar children who have not attended pre-k. While some studies have shown that the advantages persist well into elementary school, two reports have led some policymakers to question whether pre-k can provide the persistent effects that undergird an ambitious agenda for pre-kindergarten programs. Previous studies have found positive impacts on children's skills at the end of the pre-k year but not later in elementary school. These findings have caused policymakers and educators to turn to the scientific community for clarification about the likely impacts of pre-k programs and identification of those factors that might distinguish effective early learning programs. Although the early years are not the only time when a child's development can be influenced, evidence suggests that the year before kindergarten is an opportune period. In order to understand how to use the new phenomenon of pre-k to boost early learning and to provide a stronger base over time for skill acquisition, a Pre-Kindergarten Task Force of interdisciplinary scientists reviewed the evidence on the impact of state-funded pre-kindergarten programs and set out to bring science to bear on the current state of knowledge and it's implications for the path forward. The report begins with a description of the pre kindergarten landscape in America today. Another group took in all available information, reached consensus on the six major conclusions that form the basis for this report. A consensus statement summarizes the findings. Subsequent topical chapters commissioned and authored by individual scholars offer insights to assist policymakers in reaching decisions. They provide fodder for future scholarly inquiry, and are provided here. Following an overview and introduction, the following are included: (1) The Current Landscape for Public Pre-Kindergarten Programs (Ajay Chaudry and A. Rupa Datta); and (2) A Consensus Statement: Puzzling It Out. The Current State of Scientific Knowledge on Pre-Kindergarten Effects (Deborah A. Phillips, Mark W. Lipsey, Kenneth A. Dodge, Ron Haskins, Daphna Bassok, Margaret R. Burchinal, Greg J. Duncan, Mark Dynarski, Katherine A. Magnuson and Christina Weiland). "Issues and Challenges" presents: (3) Do Some Groups of Children Benefit More Than Others from Pre-Kindergarten Programs? (Helen F. Ladd); (4) Do Pre-Kindergarten Curricula Matter? (Jade Marcus Jenkins and Greg J. Duncan); (5) Characteristics of Pre-Kindergarten Programs That Drive Positive Outcomes (Dale C. Farran); (6) Universal vs. Targeted Pre-Kindergarten: Reflections for Policymakers (William Gormley); (7) The Costs and Benefits of Scaled-Up Pre-Kindergarten Programs (Lynn A. Karoly); (8) Challenges to Scaling Up Effective Pre-Kindergarten Programs (W. Steven Barnett); (9) The Promise of Preschool Education: Challenges for Policy and Governance (Ajay Chaudry); (10) Financing Early Childhood Programs (Ron Haskins); (11) Reframing Early Childhood Education: A Means to Public Understanding and Support (Craig T. Ramey and Sharon Landesman Ramey); and (12) Bibliography of Studies on the Effects of State- and District-Funded Pre-Kindergarten Programs for the Consensus Statement. A list of contributors is also provided. (Additional funding for this report was provided by SAS Institute.)