Stuart Palmer's delightful schoolteacher sleuth, Hildegarde Withers, made quite a name for herself in the movies. As mentioned in some of the comments on my post about "Murder on the Blackboard," a number of movies were made from Palmer's books, starring Edna May Oliver as Hildy and James Gleason as her friend and foil, Inspector Oscar Piper.
I haven't seen any of the movies lately, but Oliver is said to have been perfect in the role. That's not surprising, as she was one of Palmer's inspirations for the character, after he saw Oliver on stage in the first run of the Kern/Hammerstein/Ferber musical "Showboat" (according to Tom and Enid Schantz's introduction to "Murder on the Blackboard").
As best as I can tell, the movie version of "Murder on the Blackboard" isn't easily available, although TCM, Turner Classic Movies, apparently runs it from time to time. Here's a link to the TCM page describing the movie; I'd warn against reading the full synopsis there, however, as it gives away the entire plot. If you want more information about the movie, here's its page from the International Movie Database.