School readiness includes the readiness of the individual child, the school's readiness for children, and the ability of the family and community to support optimal early child development. It is the responsibility of schools to be ready for all children at all levels of readiness. Children's readiness for kindergarten should become an outcome measure for community-based programs, rather than an exclusion criterion at the beginning of the formal educational experience. Our new knowledge of early brain and child development has revealed that modifiable factors in a child's early experience can greatly affect that child's learning trajectory. Many US children enter kindergarten with limitations in their social, emotional, cognitive, and physical development that might have been significantly diminished or eliminated through early identification of and attention to child and family needs. Pediatricians have a role in promoting school readiness for all children, beginning at birth, through their practices and advocacy. The American Academy of Pediatrics affords pediatricians many opportunities to promote the physical, social-emotional, and educational health of young children, with other advocacy groups. This technical report supports American Academy of Pediatrics policy statements "Quality Early Education and Child Care From Birth to Kindergarten" and "The Inappropriate Use of School 'Readiness' Tests."