Over 95% of public schools in Japan have started using digital devices for learning. Previous studies examined the effects of on-demand classes compared with face-to-face (FTF) classes on grades in adults, but the results were inconsistent. In addition, no studies have examined the immediate effects or included children. While improving these problems, this study aimed to examine the immediate effects of on-demand classes on children's learning and brain activities. Four subjects completed the experiments and were included for analysis. Teachers and students’ cerebral blood flow changes in prefrontal cortex (PFC) during an 18-minute math class were measured with near-infrared spectrometer (NIRS). Every subject took one FTF class and one on-demand each. After each class, they took a comprehension test. Learning efficiency and brain activity were compared between two conditions. This research is conducted with the approval of the Ethics Committee of the Graduate School of Medicine, Tohoku University.Our findings indicate that the percentage of correct responses following face-to-face (FTF) instruction (average of 66.6%) was comparatively higher than that after on-demand sessions (average of 57.2%). We found that FTF shows greater brain activity than on-demand in medial PFC (FTF (mean = 0.0344 mmol × mm) > on-demand (mean = 0.0220 mmol × mm)) and lateral PFC (FTF (mean = 0.0299 mmol × mm) > on-demand (mean = 0.0101 mmol × mm)).These findings offer scientific proof that brain activity plays a crucial role in children's learning, and face-to-face (FTF) instruction outperforms on-demand methods in terms of learning efficiency.