Students usually choose and begin a course of study prior to enrolling in the ninth grade. Because academic backgrounds and preparedness of students vary, some may begin their course of study before or after their ninth grade years. Many factors such as character, maturity, and health effect individual productivity. Students are encouraged to do whatever is necessary to complete their course of study for each year. Some students choose to do extra assignments at home, spend more time in school each day, go to summer school, or opt for lengthening their time in high school. If students qualify, they may be concurrently enrolled in college courses.