This study evaluated the worksheets used in the Sustainable Development Goals (SDGs) Challenge Project from the students' perspective and identified requirements for teaching materials to help students who are unfamiliar with design-based learning learn about the SDGs. We analysed students' and teachers' feedback in worksheet surveys. The findings revealed that the ideation process was the most difficult aspect for high school students. The reported reasons were categorised as originality, idea diversification, idea convergence, consistency with problems, feasibility, specificity, iterability, complexity, and procedure. Teachers mentioned that students did not sufficiently focus on problem identification, causing subsequent difficulties in the ideation process. Teaching material should meet the following requirements: (1) demonstrating methods for diversification and convergence of ideas to specify scaffolding, (2) clear goal setting in the problem identification process, and (3) iterability to allow for change according to the design process.