Like, I presume, most authors of nonfiction, I am a back matter groupie. The back matter is not in the back because it's dull, on discount, or less important. It's there because it serves a different purpose than the front matter (AKA the story proper): enhancement.
By that I simply mean that the back matter would lose most or all of its meaning without the front matter. It elaborates on the narrative you’ve just read, so logically it must follow it.
And there is just as much room for variety of approach back there as in any narrative.
In nonfiction picture books, back matter typically consists of some or all of the following:
- author's (and sometimes illustrator's) note/afterword (What is the difference between an author's note and an afterword? Without having researched this, I don’t know if a concrete answer exists, but here's a paraphrase of one my Boys of Steel: The Creators of Superman editor Janet Schulman offered: an afterword continues/concludes the story, often bringing readers to the present day or even beyond, whereas an author's note comments on the story or reveals backstory. Author's notes are often depositories of irresistible anecdotes that wouldn't have flowed within the story proper.)
- selected sources (sometimes called works cited or bibliography; I prefer "selected sources" to clearly indicate you’re not able to list all)
- further reading/exploring (may overlap with selected sources and can include books, sites, museum exhibits, and so on)
- photographs (especially fun when in back matter of illustrated nonfiction picture books so readers can compare the illustrations and the "real" thing)
- glossary (though I agree with Susan E. Goodman's comment on Deborah's post: the space is better used with other material you can get from only that author)
- timeline (though I often feel this also isn't worth the real estate because the major beats are already presumably covered in the story proper)
- list of works/accomplishments of the person/people profiled (say, recordings of a musician or season-by-season stats of an athlete)
In Boys of Steel: The Creators of Superman, I ended the story proper in 1940—only two years after Superman debuted, when he was top of the world. I "finished" the story in the afterword, at a higher reading level.
I did this because people who have even vague familiarity with comics history before reading the book know that Jerry and Joe's story doesn’t have a happy ending: the Boys of Steel had sold all rights to Superman…for $130. That fateful decision sets the downbeat tone that almost always permeates the telling of their story. For much of their adult life, the Boys fought against The Man for a greater (fairer) share of the profits Superman generates; they eventually got something, but most feel it was too little, far too late (it took more than 35 years!). It's bleak stuff. And kids can handle it…but I didn’t want that to be the thrust of the book.
I felt the Boys deserved a telling that, for once, ended on a high note. After all, they created the ultimate American symbol of hope…