Participation in high-quality preschool can improve academic, behavioral, social-emotional, and cognitive outcomes for students of varying backgrounds, including students from disadvantaged backgrounds (e.g., Andrews, Jargowsky, and Kuhne 2012; Barnett 2008; Camilli et al. 2010; Karoly and Bigelow 2005; Reynolds et al. 2007). However, some studies have found that some of these benefits do not persist into third grade (e.g., Bogard and Takanishi 2005; Li et al. 2013; Lipsey, Farran, and Hofer 2015; Puma et al. 2012). Without additional and continuous supports as children proceed through the elementary grades, participation in preschool does not inoculate against the potential challenges that children, particularly children at risk for poorer academic outcomes, may face. To explore how educators might build on and sustain the positive effects of preschool, this study examined two types of strategies that preliminary literature searches revealed as promising practices to support children's learning in early elementary school: (1) aligning instruction from preschool through grade 3 (referred to as P-3 alignment) and (2) differentiated instruction. The P-3 alignment strategy emphasizes coordination among standards, curricula, instructional practices and environments, student assessment, and teacher professional development between the preschool years and the early elementary school years. The differentiated instruction strategy focuses on teachers varying their pedagogical practices to meet the diverse needs and skills of individual students. To explore how educators use these two strategies, this study conducted a systematic literature review followed by case studies of five programs that used one or both of these two strategies. The case studies focused on the approaches programs used to implement P-3 and differentiated instruction; some of the approaches revealed may be relevant to early elementary strategies beyond the two strategies studied. This report focuses on the findings of the case studies. Key Findings: (1) All five case study programs aligned instruction across grades by aligning or coordinating standards, curricula, instructional practices, and professional development; three sites also used aligned assessments; (2) Common elements of P-3 programs included the use of professional learning communities (PLCs), coaches, parent engagement, and play-based or student-initiated learning; (3) Although only one site was explicitly nominated for the study for its differentiated instruction approach, teachers in all five programs reported using strategies to accommodate students' different skill levels, including modifying assignments, adapting learning materials, providing different levels of support, or using small-group instruction; (4) All five programs focused on increasing students' vocabulary, oral language, and social-emotional skills; (5) Staff in four programs reported that they had observed improvement in students' vocabulary or oral language skills, social-emotional development, and engagement or attendance, as well as increased parent involvement after implementing their programs. Initial evaluations or outcome studies from Chicago Child-Parent Centers (CPC), Early Works, and Sobrato Early Academic Language (SEAL) program support many of these perceived changes; and (6) Staff in all five programs reported that guiding teachers to change their practices in the context of P-3 alignment (e.g., incorporating student-initiated learning) was a challenge, and staff in all five programs reported concerns about funding sustainability. The report includes the following appendices: (1) Methodology; (2) Interview Protocols; (3) Observation Guide; and (4) Analysis Codebook. [For "Results in Brief: Case Studies of Schools Implementing Early Elementary Strategies--Preschool through Third Grade Alignment and Differentiated Instruction," see ED613387.]