So, this is partly inspired by @anthurak's posts on the subject, but...Jaune's struggle is really a hell of his own making. Not just because he tried to skip the line and go to Beacon without combat experience, but because he doesn't seem to be working all that hard at being a Huntsman once he gets there!
Like, the first class we see him failing at is a combat one, but then we get a prolonged scene with him screwing up in history with Oobleck. And the thing is, that's a totally mundane subject — Jaune shouldn't be at a disadvantage there! Assuming he had a normal and stable school life (rather than, idk, terrible homeschooling) before attending Beacon, I actually think he'd probably be in better shape academically than a lot of his peers.
(Ren and Nora might have gone to combat school, but they also might've just lived on their own with no stability or formal education until Beacon. And Blake has lived in isolated terrorist camps for the last five years, so even if her childhood education was excellent and she's a bookworm by nature, she had to have missed some common-core stuff.)
But Jaune is failing a history class...right up until Cardin threatens him, it seems like. Because then Jaune gets blackmailed into doing all of Cardin's homework, and seemingly succeeds? Granted, direct blackmail is a greater incentive to do your homework than just bad grades. (I wonder if the fraud and taking up a spot at one of the very competitive Huntsman Academies — of which there are four in the entire world — is not just an expulsion kind of crime but the jail-time type. Because that's one hell of a sword of Damocles to have swinging over your head.) I'm also betting Jaune's own grades took a hit, since he probably didn't do every assignment twice over, once for himself and once for Cardin, and turn out something great both times. He wasn't actually doing good work twice, only once, but that's still more than he was managing sans blackmail.
Anyways. My point: if Jaune doing all of Cardin's homework was resulting in bad grades for Cardin, then Cardin would've threatened Jaune further, or just exposed him outright. Jaune doing Cardin's work was getting at least a C-average, meaning Jaune could've dragged himself up that much, at least academically, by himself! He didn't need help, he needed motivation.
BUT. I think I know why Jaune was failing even the academic subjects he should've been able to pass. It was because he was so deeply disconnected from the reality of being a Huntsman.
I mean, we knew that he didn't know what it took as soon as he admitted he cheated his way into Beacon. That he used fake transcripts and never actually went to combat school or learned to fight. But to cut more to the point, I don't think Jaune had ever really thought about the reality of being a Huntsman — that as Team RWBY say in Volume 2, it is a job. One that takes knowledge and practice and technical skills as well as combat training!
Because...well, look at what Jaune says when he explains himself to Pyrrha, citing his family as the reason for his choice.
"They were all warriors, they were all heroes! I wanted to be one too."
Jaune says his father and grandfather were warriors and heroes, but not Huntsmen. He's thinking of the fantasy of the job when he applies to Beacon, not the reality of the job. He doesn't know the work or have the skills, sure, but it's not just down to effort and grit and training. Jaune also doesn't seem to understand the practicalities of what a Huntsman's job really looks like.
I want to be clear: I love Jaune as a character. He grows by leaps and bounds. But he really did start off the series living in fantasyland.