The Faculty of Architecture of Delft University of Technology considers valid and reliable assessment of designing an important issue. A project called Bottom-up was started to address this issue, using the experiences and practice of design teachers as a starting point. The goals of this project were to enlarge inter-subjective reliability and to develop a common focus on learning goals and assessment of designing by teachers. The core of the Bottom-up project consists mainly of design teachers talking together about designing and the assessment of designing. The article describes the process of defining assessment criteria and the assessment criteria themselves. These criteria are placed within a theoretical framework of designing as problem-solving. (Contains 2 figures.)