This study examined preservice teachers' (PSTs) capacity for lesson planning in a university-based teacher preparation program in the USA Participants (n = 126) wrote lesson plans in three approaches: synthesis, creation, and modification. Findings indicate that PSTs who modified preexisting lesson plans produced better lesson plans than their peers and reported higher efficacy in their use of the lesson plan in their field experiences. This study supports the notion that the efficacy of first-year teaching lies more appropriately in the area of enacting curriculum than in the area of designing curriculum. With respect to career-long learning, PSTs' abilities to do curriculum work are likely to improve, as they grow more familiar with students and existing excellent curricula over years. Although the study presents a snapshot of U.S. preservice teachers' capacity for curriculum design, the findings may serve to inform the literature on the developmental aspect of curriculum design for teacher education systems across the world.