This design research describes the development of a student inquiry project in which upper-secondary school chemistry students learn domain-specific concepts by doing inquiry in a simulated inquiry community. The design of the inquiry project is based on the extended procedural and conceptual knowledge in science (PACKS) model; the student inquiry-learning process is considered to be cyclic and iterative. Five teachers collaborated and developed a student inquiry project, Diffusion: Moving Particles. An inquiry community of 80 upper-secondary school chemistry students (ages 16-17) at four schools was established. Our data show that implementing the project improved student understanding of domain-specific concepts. Key activities included: brainstorming; prediction, observation, and explanation in a demonstration experiment; doing a guided experiment; judging an example research article; creating an inquiry plan; and reporting the inquiry findings. We hypothesize that domain-specific student learning occurs because of the authentic character of the successive inquiry actions. Further research is needed on the impact on students' domain-specific learning when they participate in a real science research community. (Contains 1 table, 3 textboxes, and 4 figures.)