Twelfth grade, senior year, or grade 12 is the final year of secondary school in most of North America. In other regions, it may also be referred to as class 12 or Year 13. In most countries, students are usually the ages of 17 and 18 years old. Some countries have a thirteenth grade, while other countries do not have a 12th grade/year at all. Twelfth grade is typically the last year of high school (graduation year).