The Worst Witch Saves the Day by Jill Murphy
It's the start of a new term at Miss Cackle's Academy for Witches and Mildred Hubble is determined not to be the worst witch this year. Everything starts so well. Mildred's class has a new form teacher - no more Miss Hardbroom for Mildred and her friends! But then the new teacher, Miss Granite, starts acting fishy; Mildred has a very bad hair day when a hair growth spell goes wrong and she has to put up with know-it-all Ethel Hallow being 'helpful'. To top it all, her beloved cat Tabby is having a nervous breakdown and refuses to fly.