How many grades are in your country's schooling system?

In the US, it's kindergarden (5-6 years old) through 12th grade (17-18 years old). It may vary by school district, but typically, elementary school is kindergarden through 5th grade (10-11 yo), middle school is 6th-8th grades, and high school is 9th-12th grades. There's also an optional 1 or 2 years of preschool before kindergarden.