I’m going to simply copy-paste my Quora answer about this because I am nothing if a lazy disappointment and an attention whore. Thanks for the mention, @fivenamereveals!! :DD
*digs out files* AAAAAAAALRIGHT, lecture time!
Okay so let’s check this out - Ron has canonically gotten only 3 detentions. He might have had more but they’re never mentioned - we never get any kind of phrase like “Ron had a detention so Harry was on his own”. Ron ever receives three detentions in the first five books: one over the Ford Anglia and two courtesy of Snape - because he defended Hermione and Harry respectively.
Ron has good grades. There’s never, in the books, any mention of Ron failing his classes or anything. He leaves his homework at the last minute but still does it. He’s not that bad a student honestly - but of course compared to Hermione everyone is a slacker.
About “Ron breaking the rules as much as Harry did”, nope. Harry is far more reckless and irresponsible - but Hermione keeps a tight leash and tries to restrain him. Ron is there to give Harry a breather and stop Hermione from taking complete control, and considering how bad a control freak Hermione is, Harry goddamn needs it. Harry always tries to rush off on his own at the first sign of danger, to take charge and to solve the problem himself. Ron is much more moderated - if it’s really a potentially lethal danger, he’ll go to an authority figure at first. Harry being prefect would be a disaster - he’d refuse to listen to adults. He’s is a dyed-in-the-wool rule-breaker. He’s distrusted authority figures all his life. His first instinct when something goes wrong is to immediately snoop around, and when a teacher forbids him to? That’s the way to ensure that Harry will snoop around.
Ron also hates bullying. He defends Neville, Hermione, Harry - really, anytime someone picks on anyone Ron barges in nostrils flared and wand at the ready. Instead of having Ron cursing everyone to oblivion, he’s given the power to hand over detentions, which is much less violent.
(Ron calling the first years “midgets” has always given me some sort of “big bro” vibe. I don’t know. I’d imagine him to be a rather laid-back prefect, not the kind you go to for homework but the kind you go to when you feel homesick.)
If Hermione is to be made prefect, it must be Ron who’s the other prefect. Ron is the only person who speaks up against Hermione, the only one who’s not afraid to fight her back, and the only one who can counteract any too-strict decision she might take. And you bet that Hermione is going to be strict and uptight as all heck.
Sadly, Ron’s main failure as a prefect comes from the fact that he’s too intimidated by his twin brothers - and that’s really, really messed up, honestly, that Ron is so afraid of Fred and George that he doesn’t dare standing up to them.
The problem here isn’t Ron’s lack of authority or whatever: it’s the fact that the twins hated Percy, and Percy was a prefect, so in the twins’ minds, Ron has now turned into another Percy; and Ron was already a favourite victim of the twins. So what’s he to do? He doesn’t fight against Fred and George, he acts meekly, he doesn’t try to impose himself on them.
Of course he should punish them, because he’s a prefect. But he also knows that if he does attempt to hold his authority over them, the twins will turn his life into a living hell. And considering how badly the Slytherins are getting to him over Quidditch, Ron really doesn’t need another blow to his self-esteem, doesn’t he?
The messed-up thing? It’s not healthy. It’s dreadfully not healthy. Treading around Fred and George, for Ron, is more of a survival thing than an actual brotherly relationship. Damn it.
Ron’s major shortcoming as a prefect is that he can’t fight against his two big brothers, so he lets Hermione deal with them. And since Fred and George are the biggest rule-breakers there is (after Harry mind you), it looks like he’s not doing anything. Blame it on Rowling.