In a novel or short story, name teachers the same way you would name any other character. Make her name fits her personality. Since teachers occupy a position of authority in the classroom, make sure her name is used with an honorific such as Mr., Mrs. or Ms.
Teachers at the college or university level are typically Ph.Ds. Ask yourself what your character is like as a teacher. Consider whether she gives out candy whenever the class answers a question correctly or whether she drags her nails across the chalkboard to wake up sleeping students. For the first character, a cheerful name such as Mrs. Beanblossom might be a good fit, while the second needs something a little more sinister, such as Mrs. Agatha Dour or Madam Screech. Try using the name of a former teacher who left you with a particularly good or bad impression. Name characters after your friends and family, or pick names out of an interesting news article. Name indexes and generator sites such as Yellow Pages, BehindtheName.com and BabyCenter's Baby Name Finder are resources that allow you to choose from over 1 million unique names. On many sites, you can search names by gender, popularity, and the language or culture of origin.