There are four divisions in the hierarchy of Science Olympiad:
Division A1 for elementary school (grades K-3)
Division A2 for elementary school (grades 3-6)
Division B for middle school (grades 6-9)
Division C for high school (grades 9-12)
Note that 3rd, 6th, and 9th graders have the option of competing in either of the two divisions in which they meet the grade requirements.