This study aimed to analyze the effect of problem-based learning on metacognitive abilities in the conjecturing process of junior high school students. To reach this purpose, a mixed-methods design, which is a combination of quantitative and qualitative methods, was used. +e quantitative method was used to analyze the metacognitive abilities of the students’ conjecturing process, while the qualitative method was used to explore observation and interview data. +e subjects of this study consisted of 60 eighthgrade students. Two learning models were compared, namely the problem-based learning model and the conventional learning model. +e metacognitive abilities of students’ conjecturing process were measured by a pattern generalization problem-solving test. After collecting the data and analyzing them through the independent-samples t-test, it was revealed that the PBL had a significant...