The Writing Center @ The University of Wisconsin - Madison
The Writer's Handbook
APA Documentation Guide

Spacing

Double-space all text throughout the manuscript, including the title page and reference page. For student papers, the APA allows some exceptions, for instance, wider spaces between text and headings, and single-spacing within reference list items and long quotations. Check with your instructor before making these exceptions.

For more information on spacing, see page 229 (standard APA style) of the Publication Manual.