The Big Shrink (Upside-Down Magic #6)

"Marigold Ramos can magically make things small--sometimes very, very small. The only problem? She can't figure out how to make them big again. Maybe a new tutor can help Marigold manage her magic. And maybe her magic will come in handy as she and her friends in the Upside-Down Magic class band together to protest a new rule by their principal, a super unfair rule that bans them from bringing their amazing new toy dragons to school"--Publisher's description.