yes, the middle school is called Chuugaku (中学) and the high school is called Koukou (高校) both take 3 years to complete. besides that the elementary school is called Shougaku (小学) and takes 6 years to complete, so 12 years to be ready to go to college ^^

True. The education in public school starts at the age of 6. We spend 6 years in elementary school, then 3 years in junior high(middle) school, then 3 years in senior high school. We don't have the concept of "grade", but if we say in the way, 1-6 in elementary school, 7-9 middle school, 10-12 high school.

Actually in Japan they say: Junior high school - 3 years. Senior high school - 3 years. If you don't make the grades you can always repeat a year. After senior high, if you don't make college, you can go to 予備校、　(prop school), and try to make the grade there.