Skipping the Last Year of High School in the USA Through Proficiency Tests

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What are the short- and long-term goals of the student?
High school in the U.S. is four years, so are you talking about the third and fourth year or just the fourth year?

There are various high school / college hybrid programs, like dual enrollment or early admission, but there are other ways to earn college credit while in high school, such as AP, CLEP, etc. One possibility to graduate early is switching to homeschool and accelerating any remaining coursework, but the rules will vary by state.