This mixed-method research aimed to determine the effectiveness and benefits; the construction of mathematical concepts through PBL and factors affecting indigenous people’s learning. The quantitative part of the study adapted the one-group pretest-posttest experimental design while the qualitative part used case study of multiple cases. The result of the pretest and posttest were used to analyze the effectiveness of PBL with the use of mean, standard deviation, and Wilcoxon Signed Rank Test. For the qualitative part, data gathered with the use of audio-video recordings of the personal interviews and observations underwent triangulation of results. The data were then transcribed, analyzed, and interpreted inductively through the patterns that emerged from the different sources by the researchers through thematic analysis. The result showed that there was an increase in the mean score of the participants after the intervention. The pretest and posttest results showed that there was an increase in the mean score of the participants from 7.39 (above average) to 8.54 (excellent). Meanwhile, there was a significant difference of 0.41after the intervention. The thematic analysis revealed how indigenous people construct mathematical concepts through PBL, the benefits of PBL and factors that affect students’ learning. The findings showed that constructing mathematical concepts through PBL included (A) Constructivism and (B) Constructionism. Moreover, it revealed that the factors that affect students learning were: (A) Literacy, (B) Availability of the resources, (C) Belief and culture, and (D) Frequent absences: transportation and parents’ occupation.