This study aimed to empirically investigate the online learning behavior of pupils in terms of learning engagement by incorporating four blended project-based learning (PBL) courses. Over 700 pupils from various countries participated in the empirical study for 10 weeks in 2019 through the Internet. Results of the study revealed that the overall statistics in online learning indicators are astonishing and they seem to imply that pupils in the program are hilarious with learning activities and also engage in an online spree. After dissecting the online learning indicators in detail in the perspective of learning analytics, it shows adverse outcomes in terms of learning engagement. The study further reveals that most of the frequency distribution of the indicators is highly skewed positively and less than one third of pupils in the program have devoted themselves in the learning tasks or actively interacted with content online. Even worse, fewer than 20% of the pupils in the program engaged in much needed peer evaluation activities or interpersonal interaction in blended PBL courses online. The study also proved that all indicators are significantly correlated to each other in reciprocal basis. Two pillars of enhancement are recommended based on results of the study for further practices of blended learning, which are refactoring the team-based learning tasks design, featuring role play assignments and providing visualization of data panels, such as a dashboard, summarizing personal learning progress and informing of learning discrepancy whenever necessary.