Twelfth Grade (also known as Grade 12, Senior Year, Standard 12, 12th Standard, 12th Class, or Class 12th or Class 12) is the twelfth and final year of formal or compulsory education. It is typically the final year of secondary school and K–12 in most parts of the world. Students in twelfth grade are usually 17-18 years old. Some countries have a thirteenth grade, while other countries do not have a 12th grade/year at all.

In Australia, the twelfth grade is referred to as Year 12. In New South Wales, students are usually 16 or 17 years old when they enter Year 12 and 17 or 18 years during graduation (end of year). A majority of students in Year 12 work toward getting an ATAR (Australian Tertiary Admission Rank). Up until the start of 2020 the OP (Overall Position, which applies only to students in the state of Queensland) was used. Both of these allow/allowed them access to courses at university. In Western Australia, this is achieved by completing the WACE; in South Australia, this is achieved by completing the SACE; in Victoria, this is achieved by completing the VCE; in the Australian Capital Territory, this is achieved by completing the AST and in New South Wales this is achieved by completing the HSC.

In Bangladesh, educational institutions offering the 11th–12th grade education are known as colleges. In the 12th grade, students study in one of the three streams: science, humanities, and business studies. After completing 12th grade, they have to sit for the Higher Secondary Certificate (HSC) examinations.

In Canada, the equivalent is Grade 12.

The twelfth grade is the third and usually last year (a fourth-year is possible) of high school or secondary school (or Gymnasium). The students graduate from high school at around 18, with some 17 or 19. The twelfth grade is shorter than previous because the twelfth graders' lessons end in February and they go on to take their final exams shortly afterward. Compulsory education ends after the twelfth grade, and it is completely optional for a student to continue into fourth-year.

The equivalent grade in France is Terminale. It is the third and last year of lycée (the French equivalent to high school), whereby students must sit a test called the Baccalauréat to complete the year. French-language schools that teach the French government curriculum (i.e. are part of the AEFE network) use the same system of grades as their French counterparts. This is not compulsory, as education in France is only compulsory until students turn 16.

In Lebanon, twelfth grade is the third year of high school, also referred to as the third year of higher secondary education, the class of seniors, or the last class of the school. Students in twelfth grade in Lebanon are between the ages of 17 and 18.

In the Netherlands, senior year is named by the school level. From low to high: "VMBO", "HAVO" and "VWO". VMBO is composed of four years, with 12th grade being the fourth (4th) and final year. A higher school level is the HAVO, which lasts for five years. The highest school level is VWO, which lasts for six years. So at the HAVO, students are considered senior if they are in "5th class", whereas at VWO, in "6th class" respectively. The last year mainly focuses on preparing for the final exams, after which students should be ready to go to college or university. Usually, 4th and 5th grade students are aged 16 to 17 and those who are in 6th grade usually are aged 17 to 18.