During the 2015-2016 school year, a total of 34,726 students were tested in Missouri. Of the 26,692 juniors and seniors that were tested, only 6.55% were tested under Option 8. The remaining juniors and seniors had their test results sent to recruiters without parental consent.
The 20 largest testing sessions assessed a total of 5,391 students. 334 sessions tested 10 students or fewer.
The ASVAB test was conducted in 512 schools across the state. 149 of these schools report that they made the test mandatory. Consequently, 8,694 students are confirmed to have been required to take the ASVAB; there may be more, judging from the numbers in some schools. See Missouri's database here.