Using an inquiry project-based learning (PBL) approach that involved the collaboration of three kinds of teachers (general studies, language, and information technology [IT]) and the librarian, primary 4 students from a Hong Kong school were guided through group projects. The effect of this approach was examined by comparing the project grades of students who took part in the inquiry PBL project with those of a control group. Surveys and interviews were conducted with students (N(1) = 141), parents (N(2) = 27), and teachers (N(3) = 11). The comparison of group project grades revealed significantly higher scores for the inquiry PBL groups (p < 0.05). Surveys showed that students were perceived to have improved in eight dimensions of learning, with no significant differences (p > 0.05) between students, parents, and teachers. Students enjoyed the projects and perceived them to be relatively easy. Gender differences and academic abilities had no significant moderating effects on the learning dimensions. Examination of the approach showed the collaboration between the four teaching staff to be effective through the support of the school administration, an inquiry learning expert, and parents. On the other hand, the main limitation was the extra workload for the teachers. Nevertheless, the study participants and stakeholders all advocate the continued implementation of the approach.