APA Citation - Quick Guide to 7th edition (2020)

Citing book chapters is a bit different from citing books or articles in that there are two sets of authors/editors. The first is the author(s)/editor(s) of the CHAPTER, the second is the author(s)/editor(s) of the book.

Let's go back to the purposes of citation - one of them is to enable others to find the material you are citing. So if you are citing material from a chapter, it is NOT helpful to the reader to cite only the book - they don't know where the cited material is within the book.

Sometimes a chapter is written by author(s) who are also the author(s) of the book. One would still cite the chapter so that the reader can locate the cited material.

More typical is that an authored chapter is in a book edited by editor(s).

In either of these cases, the chapter author(s) and chapter title are presented first, and in the same manner as for articles and books, i.e., last name followed by initial(s). The book author(s)/editor(s) are presented second, and the author/editor information is presented initials first, followed by last names. The page numbers of the chapter follow the book title, followed by the publisher.

BOOK CHAPTER IN AUTHORED BOOK: in Reference list

Prevatt, F., & Levrini, A. (2015). Case study: ADHD coaching with a young adult with comorbid mood disorders. In F. Prevatt & A. Levrini, ADHD coaching: A guide for mental health professionals (pp. 189-205). American Psychological Association.

BOOK CHAPTER IN AUTHORED BOOK: In-text citations (parenthetical and narrative)

A case study (Prevatt & Levrini, 2015) found...

Prevatt and Levrini (2015) found...

Note that the ampersand "&" is used in parenthetical in-text citations, while the word "and" is used in narrative in-text citations

BOOK CHAPTER IN AN EDITED BOOK: In Reference list

Stahmer, A. C., Wong, C., Segall, M. J., & Reiner J. (2020). Fostering inclusion with peers and in the community. In Y. Bruinsma, M. B. Minjarez, L. Schreibman, & A. C. Aubyn (Eds.). Naturalistic developmental behavioral interventions for autism spectrum disorder (pp. 99-119). Paul H. Brookes Publishing.

BOOK CHAPTER IN AN EDITED BOOK: In-text citations (parethentical and narrative)

In a study on peer interactions, Stahmer et al. (2020) found...

Stahmer et al. (2020) found...

Note that it is the authors of the CHAPTER that are cited in-text.
In this particular case, there were more than three authors, so the "et al" is used. If there were one or two authors, all the CHAPTER authors would be presented in the in-text citations.