Using data from the SELS(Seoul Educational Longitudinal Study), this study presented changes in academic achievement of students over a three-year period from 10th to 12th grades, and explored the influence of type of high school attended. The data were analyzed using the multilevel latent growth model. Results of the basic model for each school type showed that the initial achievement of students in the Special Purpose High School(SPHS) and Autonomous Private High School(APHS) students is higher than those in the General High School(GHS), but the gaps in math and English achievement between the students in the SPHS and APHS increase over time. It suggests that the academic disparity between high- and low-achieved students in both types of school may widen across grades. Based on these results, it is inferred that students who are located in the bottom rank as they go to selective schools such as the SPHS and APHS, but could be in the top if they went to the GHS, may be gradually getting worse their achievement level. The whole model, which examines the difference among the types of school, provided that female students were relatively high in the growth rate of Korean and English achievement than male students, but those gaps were reversed in math. It implies that gender gap in the rate of changes may differ according to subjects. Socioeconomic Status affected only the initial achievement but not the growth rates. After controlling for all other variables, the rate of changes in achievement of students from the SPHS and APHS was significantly higher than those in the GHS. However, considering the results that the difference between students from the SPHS and APHS increases over time, the academic excellence of the SPHS and APHS are likely to be driven by the high-achieved students. It indicates that the low-achieved students in the same schools could have negative experiences through the contrast rather than the assimilation effect by their colleagues. The results of the study suggest that an common belief that attending a selective school would be beneficial to academic improvement may be a kind of phantom for the low-achieved students, not real.