Teachers face many challenges in enacting innovative curriculum materials and often must make modifications to fit local contexts and constraints. However, without an understanding of curriculum designers' intentions, modifications can lead to a loss of coherence with respect to the embedded reform ideas of the curriculum. As new curriculum materials are used more widely, it becomes increasingly important to understand how to support teacher decision making about curriculum implementation in ways that are coherent with respect to designers' intentions.

This research posits that teachers need to understand underlying curriculum design ideas, such as the coherence of curriculum materials, which refer to the relationships between individual lessons and broader learning goals as well as connections between and across lessons that are intended to create effective learning experiences. I examined how the following three scaffolding strategies help teachers understand curricular coherence: (1) Providing visualizations to help teachers inspect multiple aspects of curricular coherence; (2) Demonstrating changes in the coverage rates of learning goals as a consequence of modification; and (3) Encouraging reflection about the modifications and their impact on coherence. The research questions addressed in this study are: (1) How does amount of teaching experience relate to teachers' understanding of coherence? (2) What are the roles of software scaffolds in helping teachers consider higher levels of coherence when modifying materials? (3) When teachers make changes in curriculum units with the assistance of software scaffolds, how do they reflect on their understanding of curriculum structure and modification strategies?

To answer these research questions, I developed a software tool as a context to support and examine teachers' curriculum modification practices. I studied twenty teachers' modification practices with and without scaffolding support. Findings indicate that: (1) Teachers' level of understanding of curriculum coherence is not related to experience. (2) Software scaffolds helped teachers consider higher levels of curriculum coherence. (3) Software scaffolds encouraged teachers to examine their understanding of unit structures and modification strategies. This study informs the design of environments that aim to support more teachers in enacting curricula congruently with respect to design intent in the context of large-scale curriculum implementation.