I'm able to follow this because I've read the LN, but for manga-only readers, I think they'd struggle a lot to figure it out.
If you do want to read it, here's an overview of what happens so that the dialogue will make more sense.
Yume is studying super hard to take first place in her class (or year). She thinks that her grades is a large part of her high school glow up, and if she loses them, she'll lose her friends and her position in the class.
Mizuto deliberately doesn't answer some of the questions on his Japanese test, to get a lower score, so that he won't beat Yume. Yume gets mad at him for patronising her, effectively. They both get mad at each other, then Mizuto stays up late (or all night) studying.