Ancestry.com recently announced an update of their yearbook collection. A quick search located a 1941 reference to my grandmother's sister, Margaret Habben, who was teaching home economics in Gridley, Illinois, in 1941.
I've found Aunt Margaret in yearbooks before, but I think this is the first time I've seen an entry with her picture. The yearbooks have been especially helpful as Aunt Margaret taught in several different schools after her graduation from Western Illinois University in Macomb and before her service in World War II.
When searching old yearbooks, don't forget to search for relatives who might have been teachers or staff as well. There are other people in yearbooks besides students.