In Canada how long do high school students stay in school?

Generally 4 years is required to receive a high school diploma. (Grade 9,10,11 12) however, there are some kids who do a fifth year. The fifth year option is usually used for students who want to re-do a course to improve their original mark, or to just take more courses. In the 4 year period, students should earn the 30 credits, needed to graduate from high school.