Math: Three years of math is required at five credits per year. Many states are requiring four credits. The standard math class for grade nine is Algebra. Students may also choose from Consumer Math, Pre-Algebra, or Pre-Calculus. The other courses are considered if a child is above or below average in mathematical skills. For instance, a below average student may take pre-algebra first while an above average student moves on to pre-calculus.
English: Four years of English is required at five credits per year. The standard English curriculum is called English I or English Grade 9. It combines grammar, writing, and literature. Many curriculums have Literature textbooks separate, but it is counted as part of the years curriculum.
Science: Three years of Science are required at five credits per year. Ninth graders study Physical Science or Earth Science. They are the same thing, but some textbooks call them Physical Science and some call them Earth Science. There really are no substitutions for this course. The only choice you have is which company you buy a textbook from. They are a little bit different, but they all teach the same principles.
History: Three years of History are required at five credits per year. Ninth grade History is usually called American History. In New Jersey you are required to study two years of United States History. I imagine most states have the same requirements. There are no substitutions just different companies and textbooks.