As videos have become one of the most common content delivery formats for online learning, tutorial-style videos have shown positive influences on student learning. Tutorial-style videos feature a tutoring session between an instructor and a student and can be used for online or flipped classroom teaching. However, past studies have been predominantly conducted in laboratory settings, and to our knowledge, only two studies were carried out in real classes and resulted in contradictory outcomes. There have been calls for replicating lab-based cognitive science studies in real classes given the immense difference between the two settings. Past studies reported some research design limitations that may have critically impacted the generalizability of the results. In this study, we addressed the limitations and implemented tutorial-style videos in a real biology online class. We found that students did learn better from watching tutorial-style videos than traditional didactic videos and the significant differences were more prominent with higher-level test questions than lower-level questions. In addition, students with medium prior knowledge learned the most from watching the tutorial-style videos than higher-achievers and lower-achievers. This result may be attributable to the shared similar mental model between the students in the videos and the students who watched the videos. Implications of implementing tutorial-style videos in everyday teaching are also discussed.