Dick's pretty good at academics, if he does say so himself. Like... not to brag or anything, but... literal genius. It's not a brag - most of the family are literal geniuses. Heck, he'll even admit Tim's probably got him beat by a few points. But, like, he's smart, okay? And he did real good in school.
And... okay. School was a while ago. But it's not like Bruce ever lets education stop. He still learns stuff. He still knows stuff! It may have been a while since his last set of exams, but that doesn't mean all that knowledge has just... leaked out or something. It's in there. He's smart.
And hey, he gets it. Tim was gonna provide sibling tutoring. Tim's kinda the family tutor, he always seems to be the one doing it. But he's got exams too. Guy's in college. And he's also got a case, and... Tim's busy, okay? And right now, his still-in-school sibling has exams coming up. Math exams, to be precise. And is kinda panicking about it. So Dick's not gonna wait around for Tim to be free, you know?
He used to be a mathlete, after all. Dick is good at math! He is not intimidated by a high-school math exam. ...Even if they've... changed how some things are done over the years. Why change math? Whatever. Math is math, the numbers make sense, the logic logics out, and he's good at math. He can totally handle a little tutoring. And hey, chance to hang out! This is prime Big Bro activity.
Also... he's pretty sure it's not the math that's the problem. Because, frankly? Kid's smart too. Another family genius, he'd go so far as to say. So he's got a theory this is more about something else. Test anxiety? School-life balance stress? Something he can prod into - gently - while he's at it, at least.
"Alright, kiddo, just breathe and show me what you're stumped on, okay? We'll get this sorted out. By the time I'm done with you, you're gonna be a math expert." Confident? Perhaps. Look, he's earned it! Mathlete! "How long we got 'til the exam?"