Research Findings: There is growing evidence that specific, teacher-led instruction and innovative instructional activities can lead to higher levels of achievement in literacy and in mathematics for young children at risk. There is limited research evidence, however, identifying professional development interventions that are effective in changing early childhood teachers' instructional practices. Practice or Policy: The purpose of this article is to examine the factors associated with early childhood teachers' ability or inability to implement a new preschool curriculum, Children's School Success, and to understand if those factors are amenable to change through professional development activities. (Contains 2 tables.)