Both Harry Potter and The Worst Witch are stories about children who attend magical schools housed in remote castles. The schools, Hogwarts and Miss Cackle's, have similar structures, teachers, and protagonists - Harry Potter and Mildred Hubble respectively. Key similarities between the schools include houses for different types of students, stern but fair head teachers, and classes like flying lessons. Overall, the stories parallel each other closely in terms of plot, tone, and charm centered around children learning magic.