Mr Majeika by Humphrey Carpenter
As a rule, magic carpets don't turn up in schools, but this is exactly what happens when Class Three's new teacher flies in through the classroom window and lands on the floor with a bump.
Mr Majeika can behave just like any ordinary teacher if he wants to, but something has to be done about Hamish Bigmore, the class nuisance, and so he uses a little magic to turn him into a frog. And to everyone's delight it looks as if Hamish will have to remain a frog because Mr Majeika can't remember the spell to turn him back again! With Mr Majeika in charge, suddenly life at school become much more exciting - there's even a magic-carpet ride to Buckingham Palace!