Abstract: During the pandemic, online learning had replaced the role of traditional in-class learning. While there are declarative studies examining advantages and disadvantages of online classes, there is a lack of evidence of the effect of online learning on objective, physiological indicators. Little is known about attentional mechanisms related to acquisition of information during online classes. The aim of this study was to examine the effectiveness of information assimilation during online lectures by recording visual attention distribution in natural, ecological learning settings. During online lectures, we monitored students’ eye movements via a computer webcam. After the lectures, students (n = 24) completed a knowledge test and reported their level of concentration and cognitive load during the lecture. The results showed that students who recalled more information from the lectures looked longer at the presentation and the lecturer, than on their image and other students, compared to students who remembered less from the lecture. Fixation duration, which is an indicator of visual processing depth, was longer for those who memorized more from the lecture. Finally, the knowledge test score was positively correlated with students' focal attention. The results can be used in designing interfaces to help students focus on relevant information, or real-time recommender systems informing teachers about the level of student concentration.