This chapter examines the complex relationships between early childhood education programs and child development research. A context for this examination is provided by a case example: the relatively new and still evolving, Vygotskian-influenced tools of the mind curriculum. After an overview of the functions and limitations of developmental theory and research in relation to early childhood education, the chapter focuses on two educationally relevant areas: the development of cognitive essentials, specifically children’s representational thinking, self-regulation, and planning, and the development of emotional competence, specifically emotional security and emotion regulation. Principles and research related to the assessment of young children’s development and learning are reviewed, with emphasis on assessment within classroom environments. The practical, systemic and policy challenges of linking developmental theory and research with early childhood curriculum and teaching practices are the focus of the final section of the chapter, including the challenges of taking a demonstration program to scale, issues of variability and quality in the system of U.S. early care and education, issues in delivering professional development, challenges of maintaining integrity and coherence, expectations for evidence and accountability, and gaps in the field’s knowledge base. The chapter concludes with a summary and recommendations for linking research with practice.