This study investigated the use of interdisciplinary learning activity task to construct students' knowledge in Mathematics, specifically on the topic of scale drawing application. The learning activity task involved more than one academic discipline, which is Mathematics, English Language, Art, Geography and integrating the Brunei Darussalam national philosophy of the Malay Islamic Monarchy. A quantitative method using a pre-experimental design focusing on one-group pre- and post-test design was used for this study. The participants were selected from a convenient sample of 43 Year 9 students in one of the secondary schools in Brunei. The findings were also triangulated with the students' collected reflective journal artifact documents. Each student journal was analyzed using the identified learning activity stages within the RBC-model, where the R denotes "Recognizing," B is "Building with" and C means "Constructing." The results showed an improvement in the students' achievement, and they were able to construct the mathematics knowledge by means of collaboration among group members. Based on the findings, it is recommended that Mathematics teachers be encouraged and supported to design authentic and interdisciplinary learning activity that are learner centered catering to the different needs of our students and also to meet the 21st century skills demand.