Empirical evidence that horizontal alignment of policies and practices from preschool through the early elementary grades sustains the effects of quality preschool and contributes to children's learning is scarce, as discussed above, but there are nevertheless good reasons to expect benefits to such alignment. Moreover, many districts and schools in California and throughout the country are working to strengthen preK-3 alignment. The purpose of this report is to document: 1) how key district and policy leaders in California conceptualize preK-3 alignment; 2) what kinds of policies and practices districts have implemented to achieve alignment; 3) what kinds of efforts and practices have been successful and the critical ingredients of their success; and 4) the main barriers districts and schools have encountered when attempting to achieve horizontal alignment between preschool and the elementary grades. To achieve this goal, we conducted interviews with individuals across the state. (author abstract)