Preaching to the chickens : the story of young John Lewis / Jabari Asim ; illustrated by E. B. Lewis. (OCLC #936192120)
Records for juvenile books often include additional fields to aid with selection. Intended audience may be encoded in the fixed fields:
Audn: j (juvenile, age 0-15)
There is also a repeatable note field 521 (“Target Audience Note”) which can use free-text description, like:
521 __ ǂa Elementary Grade
Or a rating from a specified source or scale:
521 8_ ǂa 840 ǂb Lexile
The Lexile framework assigns reading difficulty scores to books based on quantitative factors like sentence length, which may have odd results. This book, for example, is recommended by reviewers for grades 2-5, but has a Lexile score of 840, suggesting that the difficulty is appropriate for 5-8 grade.