Design and Technology Education is an excellent vehicle for the development of the so-called 21st-Century skills, such as creativity, critical thinking and cooperation. However, the development of these skills through design projects does not yet reach its full potential. Formative assessment is able to support the learning of 21st-Century skills. In a case study a teacher shares and clarifies the goal of divergent thinking with her class of 11- and 12-year old's using a newly developed interactive approach. Small drawings were made collectively to visualize the skill. Half-way during the brainstorm session, students were asked to assess their brainstorm results and divergent thinking skills in a collective reflection. The results show that the interactive visual approach led students to understand how to be successful in divergent thinking. They collectively developed expressions to talk about how sound divergent thinking looks and this enabled them to diagnose strengths and weaknesses in divergent thinking. All interviewed students reported an improvement in divergent thinking after the collective reflection. This indicates that active involvement of students in clarifying learning intentions enables the development of relevant feedback. Although this result was only achieved in one class with one particular teacher, it underlines the value of the interactive visualization tool. Furthermore, it shows that the formative assessment strategy of sharing, clarifying and understanding learning intentions and success criteria related to 21st century skills in the context of real-life design projects supports self-evaluation and feedback uptake.