An example of a teacher's farewell speech to outgoing students, by English teacher, David McCullough, Jr., of Wellesley High School, made headlines in 2012 for being brutally honest in announcing to students that they were not special. A more traditional speech might include individual farewells and references to past challenges and triumphs.
The individual farewells should touch upon a trait or specific memory that you appreciate about the student. For instance, if a student asked tough questions, they may be personally congratulated for their positive influence on inspiring class discussions. Other past triumphs might include initially challenging moments, such as a heated class discussion that led to a positive outcome, bringing the class closer together.