This study reports on a way to address twenty-first-century skills in mathematics education by organizing one-day mathematics challenges in the Netherlands. During such a day, students work in teams in school on an open-ended problem which aims to elicit skills like problem-solving, modeling, collaboration, and communication. The framework and the methodological approach of the maker movement are used to describe and analyze the design of these learning spaces for students and the practices they become engaged in. In this study, two design teams are interviewed and two assignments, including student work, are analyzed. The results show that the maker perspective bears similarities with the problem-solving perspective, but also enriches the problem-solving perspective by emphasizing the importance of tinkering, making something, and working as a community of practice. Emerging task characteristics that afford students' making processes are the use of a context that is meaningful for students, the low-floor-high-ceiling character of the open problem, and the request for a product. The extent to which the requested product is more context-related or more mathematical depends on the intentions of the task and the interest of the target group. Maker characteristics of the design teams elicit the importance of brainstorms with professionals, time for tinkering with the problem situation, and time for exploring possible student strategies, before the final assignment is developed.