Existing learning design languages are pedagogy-neutral. They provide insufficient support to explicitly represent pedagogy-specific approaches such as problem-based learning (PBL). As the first step towards pedagogy-driven learning design, we developed a PBL design language and an associated authoring tool by adopting a domain-specific language (DSL) approach. The language and the tool provide means for teachers to think and represent their own PBL designs in vocabularies that the teacher daily uses to describe their PBL approaches. This paper presents a case study to investigate whether the language and the tool can facilitate the design of a PBL course plan. Although participants had minimal knowledge of PBL and were not skilled in process modeling, after a short training they were able to prepare their own PBL course plans using the PBL authoring tool. They reported that the vocabularies in the PBL design language were easy to understand. Some thought that the tool provides flexibility and others did not think so. Nevertheless, some found the process somewhat difficult to represent the narrative into a course plan. In addition, most participants found that the tool is user-friendly and easy to learn.