Mock-ups are models or prototypes used to test designs before full implementation. They allow users to provide early feedback through low-cost, low-fidelity representations of designs made from materials like cardboard. This helps designers identify needed changes before substantial work is completed. Mock-ups also facilitate discussion between designers and users as designs can be easily modified using common tools. The document describes a mock-up of a calendar application made for children to obtain early feedback and a website mock-up as examples. The goal of the study was to develop a student problem-solving assessment model for design activities using a rubric and critical incidents, with mock-ups providing a framework.