The Worst Witch and The Wishing Star (Complete Adventures, #7)

Mildred, notoriously the worst witch at Miss Cackle's Academy for Witches, makes a wish on a shooting star - and to her great surprise it comes true! But it also spells trouble. Mildred's wish-come-true is a small dog but she has to keep him a secret from her friends, and especially the formidable Miss Hardbroom.