Many Western researchers have found that the gaps in the learning progress between students from different socioeconomic statuses primarily occur due to the accumulated effects of long summer vacations, rather than during the school years. However, it remains to be seen whether these findings can be cross-culturally applied to children in Taiwan. This study conducted four waves of surveys on students in the seventh to 12th grade. The Taiwan Education Panel Survey and latent growth curve modeling were used to conduct a longitudinal study for the exploration of the effect of summer learning and after-school learning on the learning achievement gap between high school students with different family socioeconomic statuses in Taiwan. The research results showed that the higher family socioeconomic status the adolescent students have, the more summer or after-school learning they would participate, and also the higher self-expectations they would have, which would further help them to achieve better learning performance in their adolescence and result in a higher growth rate of learning than their counterparts of low family socioeconomic statuses. Unlike the results of seasonal learning studies in West, students from Taiwanese families with a high socioeconomic status not only receive learning advantages during the summer but are also supported by additional after-school learning, tutoring, and activities during the academic year, which allows them to continue increasing the gap with students of low family socioeconomic status.