Keeping Pace by Laurie Morrison

From Amulet Books:

Laurie Morrison’s Keeping Pace is a poignant middle-grade novel about friends-turned-rivals training for a half-marathon—and rethinking what it means to win and what they mean to each other.
  
Grace has been working for years to beat her former friend Jonah Perkins’s GPA so she can be named top scholar of the eighth grade. But when Jonah beats her for the title, it feels like none of Grace’s academic accomplishments have really mattered. They weren’t enough to win—or to impress her dad. And then the wide, empty summer looms. With nothing planned and no more goals or checklists, she doesn’t know what she’s supposed to be working toward.
 
Eager for something to occupy her days, Grace signs up for a half-marathon race that she and Jonah used to talk about running together. Jonah’s running it, too. Maybe if she can beat Jonah on race day, she’ll feel OK again. But as she begins training with Jonah and checking off a new list of summer goals, she starts to question what—and who—really matters to her. Is winning at all costs really worth it?
 
Engaging and heartfelt, Keeping Pace is about wanting to win at all costs—and having to learn how to fail.