Mr. Trilby, Miss Plimsoll, and Matron
A few other teachers play minor parts in Matilda. Mr. Trilby is basically the vice principal, and he has the job of checking in on the Trunchbull after she skips town. He's a nice enough guy, and when everybody decides that the Trunchbull is really gone, he gets put in charge of Crunchem Hall.
Miss Plimsoll teaches the highest level class at Crunchem. We don't learn much about her but she seems like a challenging and fair teacher, who recognizes Matilda's abilities when Matilda's finally bumped up to an appropriate class.
And the Matron is like the school nurse, who takes care of students and teachers when they're sick, and comes to look in on the Trunchbull after her fainting fit.