The gryphon is a chimera, a mythological creature composed of different parts of other animals. Similarly, the new substitute teacher, Miss Ferenczi, is a kind of chimera. As the eNotes summary describes her:

She carries a purple purse and a checkered lunchbox, her glasses are tinted, and her hair is done up in a strange way. Before class begins, she spends time drawing a tree on the chalkboard because “this room needs a tree.”

Miss Ferenczi is the "gryphon" in this story. In the brief time she is with them, she teaches the children that there are different ways of thinking, of looking at things, and they learn to be individuals.