The success of designing software intensive systems (SISs) may be improved by incorporating experimentation to be part of the design process. This paper presents a scientific approach to experimentation on objects that are units of designers' behavior and is aimed at solving project tasks in conceptual design. The proposed approach is based on specifying the behavior units as precedents and pseudo-code programming of experiments' plans. Reasoning used by designers in the experiments is registered in a question-answer form. Experimenting is supported by a specialized toolkit.