How do I change the spacing between lines in Pages 5.5.2? Single spacing prints more like double spacing.

In the Format panel under the Text Style tab, there is a ▸ Spacing category. Click it to open, and you will have a selector that defaults to Lines, and to the right, the ability to set your spacing in decimal values. In addition to Lines, you also have At Least, Exactly, and Between capability. You can even set exact line height in points. Check that your Before Paragraph, and After Paragraph settings are correct for your needs.