You've got a student in grades 6, 7, or 8 who reads well below grade level, and the last thing they'll accept is a book that looks like a baby book. This is a shelf of hi-lo reads: high interest, low reading level. The covers look their age, the chapters are short, the plots move fast, and the words stay within reach, so a struggling twelve- or thirteen-year-old can actually finish one and feel like a reader. Any single book meets a child where they are, so hand over whichever subject grabs them.
Every book on this shelf clears the same bar: it has to look grown-up enough that a self-conscious teen will carry it, read easy enough that a struggling reader can actually finish it, and move fast enough that they want to. That's why verse and graphic novels do a lot of the work here, short lines, white space, pictures carrying the load, without ever feeling like a picture book. Pick by what your student is into: sports, a child starting over, the new child trying to fit in, a big adventure. They're loosely arranged from the most inviting first win to the most mature, but any one of them satisfies the whole idea on its own.