This study aimed to comparatively analyse the effects of problem-based learning model (PBLM) on cognitive outputs (CO). The study reviewed quasi-experimental studies on PBLM and CO, focusing on the cognitive outputs of thinking skills, problem-solving skill, and academic achievement. The quantitative data of these studies, comprising 56 articles and 14 proceedings published between 2015-2020, were statistically combined. This meta-analysis included 37 studies on the effect of PBLM on thinking skills, 20 studies on problem-solving skill, and 13 studies on academic achievement. The study revealed that the effect of PBLM on thinking skills and problem-solving skill was very high, while its effect on students' academic achievement was high. The highest effect size was reported for creative thinking, although there was not a significant difference in terms of individual thinking skill types. Tests were applied to determine whether the distribution of the effect size differed in terms of moderator variables.