Language preparation classes are an important way of teaching a foreign language with a one-year intensive program. However, they are also criticized for delaying academic studies of students. Preparation classes were also a widespread application in Turkey, where many thousands attended for one year at the start of their high school education. Science high schools in Turkey get the highest achieving students in statewide university entrance exam. Science high school students were divided into school two groups after High School Entrance Examination, and one group (1692) studied one-year language preparation and the other (1333) started their academic school year direct. Correlations and means between their HSEE entrance scores and University Entrance Exam (UEE) scores were compared to see whether there was a difference in achievement at the end of high school between the two groups. Significance of difference between correlations was calculated with Fisher’s z test and significance of the difference between means was calculated by independent samples t test. Analyses showed the group that studied one-year preparation class had lower correlations between their HSEE and UEE scores. As for the differences between means, although 2005 group had higher scores compared to the other group in the beginning, this difference decreased at the national university entrance exam conducted after four years of high school study.