Generally speaking, it is not a crime to fail a course. Good thing...were it so, I would be subject to UCMJ my self (I managed to fail a course during my career)
UCMJ stands for Uniform Code of Military Justice...it is designed to prosecute criminal misconduct.
Again, failure of a course, in and of itself, not a crime.
Now...I want to address Art 92, UCMJ, dereliction of duty
This is a provision under the UCMJ that makes it a crime (from Art 92 UCMJ)
(a) That the accused had certain duties;
(b) That the accused knew or reasonably should have known of the duties; and
(c) That the accused was (willfully) (through neglect or culpable inefficiency) derelict in the performance of those duties.
So, if they can prove, basically, that you are not trying at all. Not giving some effort? Then they could prosecute.
But that can be VERY tough to prove at court marital...if they tried to take you to NJP and you refused and demanded court, they would have to prove, basically, you did not try hard enough...and they must prove that "beyond a reasonable doubt"
If you are actually trying to pass but can not? That is not a crime.