This article discusses a comparison of the two focal primary school third-grade Korean bilingual students' language use with their previous language use when they were first-graders by examining their heritage language (HL) use at a Korean language school. For children of immigrant families in the U.S., there has been a pervasive hypothesis that their heritage language (HL) might be jeopardized due to their minimum exposure to it and its reduced status in the U.S., which can easily lead them to experience HL shift or loss (Montrul, 2018; Valde´s, 2014). However, the present study shows that the focal third graders who were attending all-English schools during the week did not appear to lose their HL. Instead, the comparison of findings indicated that they had developed a certain degree of oral proficiency in their HL, including vocabulary knowledge, thanks to the parents' involvement and practices towards their children's HL learning as well as other socio-cultural influences on the students' HL language use and development over the years.