  Preparing a lesson plan, e.g., a detailed road map with strategies and
materials for instructing a 90-minute class, is beneficial yet challenging for
novice teachers. Large language models (LLMs) can ease this process by
generating adaptive content for lesson plans, which would otherwise require
teachers to create from scratch or search existing resources. In this work, we
first conduct a formative study with six novice teachers to understand their
needs for support of preparing lesson plans with LLMs. Then, we develop
LessonPlanner that assists users to interactively construct lesson plans with
adaptive LLM-generated content based on Gagne's nine events. Our
within-subjects study (N=12) shows that compared to the baseline ChatGPT
interface, LessonPlanner can significantly improve the quality of outcome
lesson plans and ease users' workload in the preparation process. Our expert
interviews (N=6) further demonstrate LessonPlanner's usefulness in suggesting
effective teaching strategies and meaningful educational resources. We discuss
concerns on and design considerations for supporting teaching activities with
LLMs.
