Generally,the end of high school there is one year for prep.

Yes high school students from government high schools can go to uni too.College preparatory schools in the United States and Canada, commonly referred to as prep schools, are private independent secondary schools, funded by tuition fees and governed by independent boards of trustees. Prep schools may be day schools or boarding schools, or both, and may be co-educational or single-sex; however in both the United States and Canada, day schools are more common than boarding, and co-educational schools are more common than single-sex.Top-tier prep schools are known for their selective admissions process, challenging academics, and reputations for sending students to highly selective colleges and universities. Tuition fees are expensive. At some top-tier prep schools the costs are similar to attending an Ivy League university.