Abstract: A principle of early design work is to generate and manage multiple ideas, as this fosters creative insight. As computer tools are being increasingly used for early design work, it is critical to understand how their interaction models affect idea management. This paper reports results of a user study comparing how the use of three interaction models -- tab interfaces, layered canvases, and spatial maps -- affects working with multiple ideas. Designers (N=18) created and managed ideas for realistic design tasks using each model. We observed strategies for creating and managing ideas, measured process outcomes and tool interactions, and gained extensive participant feedback. From the results, we derive new lessons that can be broadly applied to improve how interfaces support multiple ideas and implemented the lessons within one model to demonstrate their efficacy.