The ASVAB is not a test to take lightly (
no pun intended) if you really are entering the service. The
military has learned one thing over its couple of hundred years of existence, and that is
don't trust civilians, especially their opinion of others, especially the kind of
loners and iconoclasts that would want to leave home and
join the Army. You may need a
high school diploma or equivalency to get in, but when they assign you your military job, they use the ASVAB results exclusively. They could care less what your grades are out there, they only care about how you scored on your military
aptitude test.
At the risk of making this a GTKY item, I'll give you an example to demonstrate my point. I had terrible grades through high school, and barely graduated. Yet based on my ASVAB, the Army sent me to USMAPS (West Point Prep) and while I was waiting for the semester to begin, they sent me to electronic warfare school to learn cryptoanalysis. (I had a motorcycle accident in my tenth month at the prep, so couldn't go on to the Academy, but I did become an intelligence analyst.)
All of this was based upon my ASVAB scores. Laugh all you want to about the Army (as I have myself, many, many times) but they seem to get the job done, and 90% of the people are in the jobs that they are suited to perform.