When his grades slip too much for regular coursework to fix, an impulsive prankster must complete community service without incident at a strict military school to graduate junior high with his best friends.

If this is an absurdist comedy, I don't think the implausible premise would be a hindrance. If it is such a farce, I suggest writing it in a way that makes it clear.

"Last thing what is at stake? What's the worst that would happen should he fail to graduate with his friends? Nothing really, he'll repeat a year and then graduate."
I agree with much of what you said, but I wonder if maybe you want stakes that are too high. The stakes are relative to the character, a realistic story about a young?boy. Does any kid?want to spend another year in school? What will that look like to his friends? His reputation will be ruined.
So, yes, the stakes are fairly low, but relatively, I think they are okay. Maybe he could add something else, but really what else can be at stake for him?
One last note, it really does seem that the only stakes films put out now are saving the world/universe.

Agree that the premise is not credible. ?If no crime has been committed, there is no legal basis to require community service. ?And it's not a crime to get poor grades. ?Nor is it a crime to be an impulsive prankster unless that entails criminal behavior. And the logline says nothing about criminal behavior.